eigenmann: the FRESHWATER FISHES OF BRITISH GUIANA 223 



Key to the Guiana Species of Plecostomus. 



a. Occipital bordered by a single nuchal plate. 



b. Length of mandibular ramus 2.4-4 in interorbital; color of upper and lower caudal lobes almost 



alike, spotted in the adult, barred in the young. Lower surface of head and body almost 

 completely covered with granules in the adult; outer caudal rays greatly prolonged, some- 

 times three times as long as the shortest. plecostomus. 



bb. Length of mandibular ramus 2 in interorbital. Lower caudal lobe dark, plain; sometimes the 

 entire caudal plain, sometimes the upper lobe spotted; lower surface naked (except some- 

 times in the largest specimens a few granular plates between the pectorals); outer caudal 



rays scarcely more than thrice the length of the middle one hemiurus. 



(bbb. Lower surface and head completely covered with granular plates in specimens 205 mm. long; 



mandibular ramus 2 in interorbital; twenty-seven or twenty-eight scutes robini.) 



aa. Occipital bordered by a median nuchal plate, and one or several small plates on each side. 



c. Caudal peduncle normally formed, the scutes of the fourth series not strongly angulated. 



watwata. 

 cc. Caudal peduncle broad and flat below, the scutes of the fourth series strongly angulated. 



emarginatus. 



90. Plecostomus plecostomus (Linnaeus). 



Loricaria plecostomus Linnaeus, Syst. Nat., ed. 12, I, 1766, 508 (America).— 

 Gmelin, Syst. Nat., I, iii, 1788, 1363.— Bloch, Ausl. Fische, VIII, 1794, pi. 

 374.— Bloch and Schneider, Syst. Ichth., 1801, 124. — Hyrtl, Denkschr. 

 Akad. Wiss. Wien, XVI, 1859, 18. 



Hypostomus plecostomus Schomburgk, Fishes Brit. Guiana, I, 1841, 139 (Rio 

 Braneo). — Muller and Troschel, in Schomburgk, Reisen, III, 1848, 643 

 (Takutu and Rio Braneo). — Kner, Denkschr. Akad. Wiss. Wien, VII, 1853, 

 263 (Ypanema; Mattogrosso; Barra do Rio Negro; Surinam). 



Plecostomus plecostomus Eigenmann and Eigenmann, Proc. Cal. Acad. Sci., (2), 

 I, 1888, 169; Occasional Papers Cal. Acad. Sci., I, 1890, 406 (Silva, Lake 

 Saraca; Para; Hyavary; -Coary; Rio Puty). — Kindle, Ann. N. Y. Acad. 

 Sci., VIII, 1895, 253 (Marajo on Rio Tocantins).— Lahille, Rev. Mus. la 

 Plata, VI, 1S95, 272 (Island Santiago).— Eigenmann and Bean, Proc. U. S. 

 Nat. Mus., XXXI, 1907, 665 (Amazon).— Eigenmann, Ann. Carnegie Mus., 

 IV, 1907, 122 (Corumba; Asuncion; Rio Apa; Arroyo Trementina); Repts. 

 Princeton Univ. Exp. Patagonia, III, 1910, 403. 



Hypostomus guacari Lacepede, Hist. Nat. Poiss., V, 1803, 145 (America). 



Loricaria flava Shaw, Gen. Zool., V, 1805, 38, pi. 101. 



Plecostomus flavus Vaillant, Bull. Soc. Philom., (7), IV, 1880, 155 (Calderon). 



Plecostomus bicirrhosus Gronow, Cat. Fish, ed. Gray, 1854, 158. — Gunther, 

 Catalogue, V, 1864, 231 , part. — Kner and Steindachner, Abhandl. K. Bayer. 



