206 ME. C. TATE REGAN ON THE 



Pkcostomus flavus Vaill. Bull. Soc. Philom. (7) iv. 1880, p. 155. 



Plecostomus plecostomus Eigenm. & Eigenm. Proc. Cal. Ac. (2) i. 1888, p. 168 ; Occ. Pap. Cal. 



Ac. i. p. 406 (1890). 

 Plecostomus seminudus Eigenm. & Eigenm. t. c. p. 169. 

 Plecostomus boulengeri Eigenm. & Kennedy, Proc. Ac. Philad. 1903, p. 502. 



Depth of body 4|~ 5 times in the total length, length of head 3-3-^ times. Depth 

 of head If times in its length, breadth of head 1^- times, length of snout If times, 

 diameter of eye 5-^-9! times, interorbital width about 2f times. Length of mandibular 

 ramus about 3 times in the interorbital width. Snout ovate, more or less narrowed 

 anteriorly ; supraorbital margins raised ; supraoccipital with moderately elevated 

 median ridge ; temporal plates carinate. Scutes spinulose, the anterior and upper 

 scutes carinate, 25-26 in a longitudinal series, 7-8 between dorsal and adipose fin, 

 13-14 between anal and caudal. Supraoccipital entirely bordered posteriorly by a 

 single scute. Lower surface of head and abdomen, in the adult, almost completely 

 covered with small granular scales. D. I 7, the first ray about as long as the head, the 

 last f— | as long ; length of base of dorsal equal to its distance from posterior -g- of spine 

 of adipose fin. A. I 4. Pectoral spine extending well beyond base of ventrals. 

 Caudal emarginate, the inner rays f— § the length of head, the outer produced. Caudal 

 peduncle 3-3^ times as long as deep. In the adult, numerous dark spots on head, 

 body, and fins, those on the head smallest, those on the dorsal in 2 rows on each 

 interradial membrane. In the young, spots on the head and body larger and fewer, 

 fins with 4-6 transverse bars. 



Total length 350 mm. 



Twelve specimens : E. Amazon ; Guiana ; Venezuela ; Trinidad. 



2. Plecostomus commersonii. 



Hypostomus commersonii Cuv. & Val. Hist. Nat. Poiss. xv. p. 495 (1840) ; Val. Voy. d'Orbigny, 



Poiss. pi. vii. fig. 2 (1847). 

 Plecostomus commersonii Giinth. Cat. Fish. v. p. 232 (1864). 

 Plecostomus spiniger Hensel, Arch. Nat. i. 1870, p. 73. 

 Plecostomus limosus Eigenm. & Eigenm. Proc. Cal. Ac. (2) i. 1888, p. 167, and Occ. Pap. Cal. Ac. 



i. 1890, p. 405. 

 ? Plecostomus aspilogaster Cope, Proc. Am. Phil. Soc. xssiii. 1894, p. 100, fig. 14. 



Depth of body 5^-5f times in the total length, length of head 3j-3f times. Depth 

 of head If times in its length, breadth of head about 1-J times, diameter of eye 8-13 

 times, length of snout If times, interorbital width 2^-2| times. Length of mandibular 

 ramus 2|~3-j times in the interorbital width. Snout rather broad, rounded anteriorly ; 

 supraorbital edges slightly or moderately raised ; supraoccipital with median ridge ; 

 temporal plates more or less distinctly carinate. Scutes spinulose, mostly carinate, 

 28-30 in a longitudinal series, 8-9 between dorsal and adipose fin, 14-15 between 

 anal and caudal. Supraoccipital entirely bordered posteriorly by a single scute. Lower 



