Guyana, located in northern South America north of Brazil between Venezuela and Suriname, includes portions of the Orinoco, Amazon, and Courantyne river basins, a majority of the Essequibo River Basin, and all of the Berbice and Demerara river basins. Partly as a consequence of historical and contemporary drainage complexity, Guyana has a remarkably diverse freshwater fish fauna. Here, we compile the first comprehensive list of Guyana's freshwater fishes, totaling some 657 species-level taxa (97 first records, 117 endemics and at least three introduced species), based on photographic records, published reports, and over 145,000 type and non-type specimens in 29 museum collections. The IUCN conservation status for each species is provided. We separately list an additional 151 undocumented species that are possibly or likely present in Guyana based on their adjacent distributions in either the Orinoco River Delta in Venezuela or the Courantyne River in Suriname. The largest holdings of fish specimen vouchers and frozen fish tissues from Guyana are housed at the Royal Ontario Museum, Toronto (ROM), Auburn University Museum, Auburn (AUM), University of Michigan Museum of Zoology, Ann Arbor (UMMZ), and the Academy of Natural Sciences of Drexel University, Philadelphia (ANSP). Additional important collections of Guyanese fishes are deposited at the Centre for Study of Biological Diversity, Georgetown, Guyana (CSBD), Field Museum of Natural History, Chicago (FMNH), Illinois Natural History Survey, Champaign (INHS), The Natural History Museum, London (NHMUK, formerly BMNH), Oregon State University, Corvallis (OS), and the US National Museum, Washington (USNM). Despite the many collections that have been made in Guyana, many species still lack vouchered specimens or tissues, and many more species require formal description.

In 1824, John James Audubon (1785–1851), painter and ornithologist, was nominated for a “corresponding” (non-resident) membership at the Academy of Natural Sciences of Philadelphia (ANSP). However, one month later, he was rejected by a vote of its resident members. This controversial event was a turning point in Audubon's career, which prompted him to abandon his goal of publishing in the United States and, instead, to seek an engraver and subscribers in Europe. Biographers have suggested that Audubon's rejection was orchestrated by George Ord (1781–1866), then ANSP Vice President, who may have felt jealous and/or threatened by his talent. However, an essay written by Ord in 1831, published here for the first time, explains that Audubon was only rejected after he was caught falsely accusing Alexander Wilson (1766–1813), the late ornithologist and ANSP member, of plagiarism and scientific fraud. Heretofore, historians have assumed that these accusations were first levied in 1839, but the primary record indicates that they were first levied in 1824. This revelation has significant implications for Audubon's biography and the history of American ornithology.

Ernst Schäfer (1910–1992) was a well-trained, highly knowledgeable and widely published German zoologist who did pioneering research on birds and mammals in Asia and South America. He was also a controversial figure, because of his association with the Nazi Party during World War II and with King Leopold III of Belgium in the 1950s. Toward the end of his life, because of the negative publicity he received for some of his ethnographic research and his association with these individuals, he became resentful of the press, and quite reclusive, refusing to talk to anyone interested in writing about his life's work.

The author of this essay was one of the few people to whom Schäfer granted an in-person interview. The essay records a wide range of topics covered during six days of face-to-face conversations in a hunting lodge in Austria in December 1986, and five years of subsequent correspondence. This is not a biography, per se, but rather a remembrance of the man, based on that interview. It is intended to complement the essay by Jorge M. González (2010) entitled: “Ernst Schäfer – from the mountains of Tibet to the Northern Cordillera of Venezuela: a biographical sketch.”

Edward Drinker Cope (1840–1897) has been lauded as America's first great evolutionary theoretician (Gould, 1977: 85), yet his religious life remains enigmatic. This paper explores Cope's Quaker background to correct popular misconceptions as to why he used singular second-person pronouns (thee, thy, thine) and numbers for days and months in his private speech, why he used guns in hunting while refusing to use military weapons or wear military uniforms, and his treatment of Native Americans as equals. It also examines why Cope resigned from the Society of Friends, his Quaker wedding to Anne Pim (1841–1933) and their later separation, and his subsequent philosophical journey.

This paper provides a catalogue of the type specimens of lice (Insecta: Psocodea: Phthiraptera) held in the collection of the Field Museum of Natural History (FMNH), Chicago, Illinois, USA. There are 178 nominal species, four of which are represented by holotype only; 14 by holotype, allotype and paratypes; 29 by holotype and paratypes; 127 by paratypes only; three by neoparatypes, and one by paralectotype. The main goal of this type catalog is to make the louse type specimens and their metadata more readily available to biodiversity researchers.

Additional material of Potadoma riperti Samé-Ekobo & Kristensen, 1985 is reported for the first time since the species was named. The new localities are near the type locality at Mikel, southeast Cameroon. All localities are in the Boumba River drainage. The species should still be considered endangered because of its small geographic range, but its status might be upgraded from critically endangered.

Tawny-crested Tanager Chrysocorypha delatrii (Lafresnaye) is a poorly known passerine bird that ranges from Honduras to Ecuador. Howell (1957) suggested, but did not demonstrate, that body size decreases with latitude. To test this hypothesis, and to review the status of a poorly known subspecies, C. d. longirostris (Huber, 1929), I collected and analyzed measurements from a range-wide sample of study skins, including type specimens (n = 203). I also performed phylogenetic analysis on a small dataset of publicly archived DNA sequences. These data confirm the existence of a morphometric cline in C. delatrii, strengthen the case for treating the complex as a monotypic species, and highlight opportunities for future research.

Loricaria thomasi, new species, is described from large and predominantly whitewater river channels draining into the middle río Orinoco. The new species is distinguished from all nominal congeners by its uniquely developed buccal tuft, a medial cluster of 25–29 simple, elongate papillae supported by a fleshy protuberance from the anterior roof of the buccal cavity, internal to premaxillae. Adult specimens of L. thomasi are distinguished from nominal congeners by having dorsal surfaces of head and anterior body relatively smooth, lacking distinct ridges or crests (vs. paired, longitudinal, odontode ridges conspicuous on supraoccipital and predorsal plates). Loricaria thomasi apparently feeds on nonbiting midge larvae (Chironomidae) in the subfamilies Chironominae (Cryptochironomus, Pelomus) and Tanypodinae (Coelotanypus) in the río Guariquito near its confluence with the Orinoco.

Three species of freshwater sponges, Ephydatia muelleri (Lieberkühn, 1856), Ephydatia fluviatilis (Linnaeus, 1759), and Heteromeyenia baileyi (Bowerbank, 1863), were collected from western Pennsylvania streams and quarry lakes in the Ohio River watershed from 2014 to 2019. This is the first literature report of these sponge species in western Pennsylvania. Identification relied on spicule morphology and was supported by barcode analysis of partial mitochondrial DNA sequences from the cytochrome oxidase subunit 1 (COI) gene. These barcode sequences could differentiate Ephydatia from Heteromeyenia but could not reliably resolve species-level identifications due to low sequence variation. All three species were found in streams with little or no silt and situated downstream from lentic bodies of water. In addition, E. fluviatilis was found in quarry lakes on substrates of various pitches but not found on top of horizontal surfaces.

A new species, Microsternarchus schonmanni, is described from a series of specimens collected in the lower portion of the Rio Pacaás Novas and Rio Mamoré-Guaporé drainages, Brazil. This is a region of high biodiversity with periodically flooded forests and savannas. The new species is diagnosed from nominal species M. bilineatus, M. brevis and M. longicaudatus by measurements including the length of caudal filament, size of mouth and eyes, and distance from snout to posterior naris. In addition, the new species differs in the higher number of anal-fin rays. Furthermore, the wider maxilla of M. schonmanni is distinguished from the more elongate maxilla of M. bilineatus, M. brevis and M. longicaudatus.

Uma nova espécie, Microsternarchus schonmanni, é descrita a partir de uma série de especimens coletados nas drenagens da parte baixa do Rio Pacaás Novas e Rio Mamoré-Guaporé, Brasil. Essa é uma região de elevada biodiversidade, com florestas periodicamente inundadas e savanas. A espécie nova é diagnosticada a partir das espécies nominais M. bilineatus, M. brevis e M. longicaudatus por medidas que incluem o comprimento do filamento caudal, o tamanho da boca e dos olhos, e a distância do focinho à narina posterior. Além disso, a nova espécie difere das demais pelo número mais elevado de raios da nadadeira anal. Ademais, o maxilar mais amplo de M. schonmanni difere do maxilar mais alongado de M. bilineatus, M. brevis e M. longicaudatus.

Moenkhausia lepidura ocoae Fowler 1943 is herein considered a valid species in Hyphessobrycon and a senior synonym of Hyphessobrycon otrynus Benine & Lopes 2008. Hyphessobrycon ocoae (Fowler 1943) was also misidentified as Hemigrammus marginatus Ellis 1911 in the older literature. We review the diagnostic features of Fowler's species which include a broad subdistal patch of dark pigmentation on each caudal-fin lobe joined vertically by dark pigment on the distal half of the middle caudal-fin rays and membranes (vs. subdistal dark patches on caudal-fin lobes completely separate in Hy. bayleyi and Hy. diancistrus or absent in other congeners). The distribution of Hy. ocoae extends across much of the llanos portion of the Río Orinoco basin in Colombia and Venezuela, and also includes historical records for Lake Valencia, an endorheic system in northern Venezuela. Of the 1,871 names proposed by Henry W. Fowler (1878–1965) for new taxa of extant fishes (not as replacement names or due to technical mistakes), about 699 (37.4%) can be considered valid at some level in 2023 compared to about 38.3% in 2011.

Hyphessobrycon ocoae (Fowler, 1943) (n. comb., n. stat.) se revalida aquí y se considera un sinónimo senior de Hyphessobrycon otrynus Benine & Lopes (2008). Hyphessobrycon ocoae también se ha identificado erróneamente como Hemigrammus marginatus en la literatura más antigua. Revisamos las características diagnósticas de la especie, que incluyen una ancha área de pigmentación oscura en cada lóbulo de la aleta caudal unido verticalmente por pigmento oscuro en la mitad distal de los radios y membranas (vs. áreas oscuras subdistales en los lóbulos de la aleta caudal separados en Hy. bayleyi y Hy. diancistrus o ausentes en otros congéneres). La distribución de Hyphessobrycon ocoae se extiende a través de gran parte de la porción de los llanos de la cuenca del Río Orinoco en Colombia y Venezuela, y también incluye registros históricos para el Lago Valencia, un sistema endorreico en el norte de Venezuela. De los 1871 nombres propuestos por Henry W. Fowler (1878–1965) para nuevos taxones de peces existentes (no como nombres de reemplazo o debido a errores), alrededor de 699 (37,4 %) pueden se considerar válidos en algún nível en 2023 (en comparación con alrededor de 38,3 % en 2011).

Type material and type localities are listed for 27 species-group taxa named by George Morgan Davis. All are freshwater gastropods and for all but two of these, there is type material in the Academy of Natural Sciences of Philadelphia. Type material of 25 taxa is illustrated herein. Davis always restricted the type series of taxa that he named to the type locality. Type material might have been cited in the original work by catalogue number or locality and, similarly, material was excluded from the type series of some taxa by citation of catalogue number or locality. For some taxa the published coordinates are corrected herein.