Fish-fauna of the Rio de la Plata. 11 



The first dorsal and pectoral rays are not spinous. Caudal 

 fin deeply forked. Coloration uniform. 



One specimen from the Parana, 13 inches long. 



25. Pimelodus sapo, Val. 



26. Pimelodus Hilarity C. & V. 



27. Pirinampus Patt, Val. 



28. Arius Commersonii, Lac. 



Very common, and growing to a length of 4 feet and more. 



29. Ageniosus milttar-is, Bl. 



30. Doras maculatus, Val. ( = Z). muricus, Kner). 



Common about the shipping, and attaining to a length of 

 more than 2 feet ; it seems almost omnivorous, greedily swal- 

 lowing the offal from ships. The stomach of one was filled 

 with large bones, probably of sheep, pieces of carrots, shells, 

 &c. 



31. Callichthys punctatuS) Bl. 



32. Plecostomus Commersonii, Val. 



33. Plecostomus alatus, Casteln. 

 Received from the Lower Parana. 



34. Plecostomus cordovm^ sp. n. 



D. 1/7. A. 5. P. 1/7. V. 1/5. L. 1. 30. 



Head very much depressed, its length being nearly two 

 sevenths of the total (without caudal) ; no ridge between eye 

 and nostril; occiput with a very slight elevation along its 

 middle ; nuchal scutes not elevated in the middle, and obtusely 

 bicarinate. The middle of the extremity of the snout is naked ; 

 mouth straight, transverse, very broad, stretching from one 

 side of the snout to the other ; labial fold rather broad, not 

 notched behind, covered with minute papilla?. Interoperculum 

 without spines. The entire lower surface of the head, thorax, 

 and belly are covered with minute scutes. The length of the 

 base of the dorsal fin is a little less than its distance from the 

 second fin ; there are ten pairs of scutes between the two fins. 

 Caudal fin obliquely marginate. The pectoral spine extends 

 to the base of the ventral, and has its extremity covered with 

 very short spines. Seventeen scutes between anal and caudal ; 

 the lateral scutes of the body with very indistinct keels, which 

 have no particular armature. Brownish black, with black 

 dots ; these are smallest and most numerous on the head, a 

 little larger on the body, and largest and least numerous on 

 the abdomen, the abdominal spots being not quite the size of 



