320 PROCEEID-INGS OF THE NATIONAL MUSEUM vox-. 94 



as fusion in the middorsal line of the plate behind the supraoccipital 

 to form a single plate in large specimens; the dorsal fin becomes less 

 hi""h and when depressed does not extend so far back in the adults as 

 in those less than 100 mm. in standard length; the spines on the 

 interopercle and distal part of the pectoral spine develop with age, 

 while the spiny keels on the plates of head and body are reduced with 

 age, almost obsolete on the head. H. maracaiboensis differs from the 

 following species in northern South America: H. landoni Eigenmann, 

 H. annectens (Regan), H. holostictus Regan, //. wilsoni Eigenmann, 

 H. schomburgkii (Giinther), and H. braueri Eigenmann, in a more 

 robust body and head, depth 3.8 to 4.0 instead of 4.75 to 8 times in 

 the species listed above. The single short hooked spine on the inter- 

 opercle among other characters helps to distinguish this species. H. 

 megacephalus (Giinther) has a smooth lower surface on body, rough in 

 the new species. 



Genus HYPOSTOMUS Lacepede 



Hijposlomus Lacepede, Histoire naturelle des poissons, vol. 5, p. 144, 1803. 

 (Type, Hypostomus guacari Lacepede =Loncana plecosiomua Linnaeus.) 



KEY TO GENUS HYPOSTOMUS, AFTER EIGENMANN (1912) 



la. Supraoccipital bone bordered posteriorly by a single nuchal plate; plates 

 along sides 25 or 26 ; ramus of lower jaw 3 times in interorbital space. 



Hypostomus plecostomus (Linnaeus) 

 16. Supraoccipital bone bordered posteriorly by a median plate and 1 or 2 or 

 more at each side; plates along lower sides 28 to 30. 

 2a. Caudal peduncle normally formed, scutes of fourth series not strongly 

 angulated; ramus of lower jaw 2.8 to 3.2 in interorbital space. 



Eypostonaus watwata Hancock 

 26. Caudal peduncle broad and flat below, scutes of fourth series strongly 

 angulated; ramus of lower jaw 3 to 4 in interorbital space. 



H3T)ostonius emarginatus Cuvier and Valenciennes 



HYPOSTOMUS PLECOSTOMUS (Linnaeus) 



Panaque 



Acipenser plecostomus Linnaeus, Systema naturae, ed. 10, p. 2S8, 1758 (ref. 



copied). 

 Plecostomus guacari Lacepede, Regan, Trans. Zool. Soc. London, vol. 17, pt. 3, 



p. 206, 1904 (River Amazon, Guiana, Venezuela, Trinidad); Proc. Zool. Soc. 



London, 1906, vol. 1, p. 389 (Paraguay to Venezuela, Trinidad). 

 Plecostomus bicirrhosus Gunther, Catalogue of the fishes in the British Museum, 



vol. 5, p. 231, 1864 (Venezuela). 

 Plecostomus plecostomus (Linnaeus) Ribeiro, Arch. Mus. Nac. Rio de Janeiro, 



vol. 16, No. 4, p. 47, 1911 (Venezuela). — Eigenmann, Indiana Univ. Studies, 



vol. 7, p. 44, 1920 (Concejo, Rio Tuy, and Rfo Tiquirito; Isla del Euro; 



Maracay, Rio Bue; Venezuela). — Pearse, Univ. Wisconsin Studies, No. 1, p. 



23, 1920 (Isla del Euro, Lago Valencia, Venezuela). — Eigenmann, Mem. 



Carnegie Mus., vol. 9, No. 1, p. 223,1922 (Lago Valencia, Rfo Tuy, Venezuela). 



—Ribeiro, Rev. Mus. Paulista, vol. 10. p. 713, 1918 (Rio Cabriale, Vene- 

 zuela). 



