168 CALIFORNIA ACADEMY OF SCIENCES. 



5. PlecOStomUS carinatUS Steindachner. 



6. PleCOStomuscommersonii (Valenciennes.) 



H. puncta'us Cuv. & Val.; H. subcarinatus Castelnau; PI. spiniger 



Hensel. 

 Localities: Kio de Janeiro; Santa Cruz; Macacos; Itabapuana. 



6a. Plecostomus commersonii affinis Steindachner. 



Localities: Mendez; Santa Clara; Kio Mncari; Rio de Janeiro; Rio 

 Doce at Linhares; Rio Paiabyba; Minas Geraes; San Antonio River. 



6b. Plecostomus commersonii scabriceps var. nov. 



Types, No. 789i. Three specimens. .30-. 35 m. Sao Matheos. Hartt 

 & Copelaud. 



h. Tip of snout naked; lat. 1. 28-30; occipital bone 

 margined by a single large luichal plate 

 i. Spots on the caudal less distinct than those on 

 the dorsal; all the scutes with high keels. 

 j. Lat. 1. 28. Eye 4J in snout, 8 in head, 3 in in- 

 terorbital; outer caudal rays little produced, 

 middle caudal rays 1^-1^ in the head. Base of 

 the dorsal fin equal to its distance from the 

 caudal, or very little shorter liniostis nov. 4. 

 jj. Lat. 1. 30. Eye 3J in snout; 6-6i in head. 



carinatus 5. 

 a. Spots on the caudal as distinct as those on the 

 dorsal. 

 k. Lower surface of the head covered with scutes. 



I. Spots all small, 12 or more on one of the 

 anterior scutes commersonii 6. 



II. Spots large, not more than 4 on one of the 

 anterior scutes. co7nmersonii affinis 6a. 



kk. Lower surface of the head naked, except a tri- 

 angular spot in front of the gill opening; spots as 

 in affinis; occipital process short. 



commersonii scah'iceps nov. 6b. 

 hh. Tip of snout granular, occasionally naked in /)Ze- 

 costomus. 



m. Lateral plates all more or less strongly 

 keeled. plecostoinus 7. 



mm. Lateral plates, scarcely, if at all, keeled. 

 Lat. 1. 27-28. 



n. Head with vermiculating light and dark 

 lines; ventral surface with short curved 

 bars. vaillanli 8. 



