384 Annals of the Carnegie Museum. 



Genus Plecostomus Gronovius. 

 8. Plecostomus derbyi, sp. nov. (Plates LXXIX-LXXXI.) 



Rare, only one example, No. 2865 (another having been eaten by 

 ants), from Porto Uniao da Victoria, taken in a trap called "cova," 

 December 27, 1909. Length 9.5 cm. to base of caudal. 



D. I. 7; A. 5; P. I. 6; V. I. 5; C. 16; depth 5.16; head 4.5 (from tip 

 of snout to humeral process); 28 scutes in lateral line; eye 4 in the 

 snout and 2.5 in interorbital space; belly about one-half covered with 

 small granules; three faint ridges on the head; humeral keels extending 

 on to base of the ventrals; no lateral keels or bony spines to scutes; 

 caudal peduncle almost rounded; similar on all sides; base of dorsal 

 longer than distance intervening between it and the adipose; last 

 dorsal ray half as long as the first; tipof the snout granular; the temporal 

 plates almost carinate; the length of the barbels about equal to 

 diameter of eye; seven scutes between dorsal and adipose fin; caudal 

 emarginate, with lower edge the longer; thirteen scutes between the 

 anal and caudal; outer edge of pectoral with many short spiny proc- 

 esses; width of head at front edge of humeral process greater than the 

 length of same from tip of snout to same place; ventrals almost as 

 long as the pectorals; all fins with rows of spots between the rays, 

 being less distinct on the caudal; ventral surface plain; dorsal surface 

 and head covered with small round spots increasing in size posteriorly. 

 In life there are three distinct and three indistinct dorso-lateral bands, 

 the ones which pass through the rayed dorsal and at base of adipose 

 being most distinct; the faint band over posterior part of head is 

 continued to form a broad bar below each eye. 



This species is characterized by the smaller eye, which is one-third 

 less in size than in P. plecostomus, by the less elevated occipital, the 

 color, and by the plates being more numerous than in P. plecostomus, 

 from which it has apparently been evolved after an accidental arrival 

 above the Iguassu Falls. 



It is with great pleasure that I name this species in honor of Dr. 

 O. A. Derby, who has spent thirty-five years in the cause of science 

 in Brazil, and who rendered me more assistance than any other man 

 in South America. A great deal of the success of the Expedition 

 of the Carnegie Museum to South America is indirectly due to Dr. 

 Derbv. 



