11. JENYNSIA. 331 



Valenciennes mentions rigid papilte on the tongue and palate as 

 a specific character of Orcstias mulleri, by which he distinguishes it 

 from the other species. I find these papillae in all young examples, 

 but never in adult ones. 



6. Orestias luteus. 



? Orestias luteus, Cuv. ^ Vol. xviii. p. 243. 



D. 14. A. 13. L.lat.39. 



Body rather stout, neck slightly arched ; head three-fifths as long 

 as high, its length being contained thrice and a fourth in the total 

 (without caudal). Eye of moderate size, not much less than one- 

 third of the length of the head in a specimen 3^ inches long. Snout 

 of moderate length, shorter than the eye, slightly obtuse, the lower 

 jaw being somewhat obliquely dij-ected upwards; pr^orbital sub- 

 quadrangular, deeper than long, without pores. Scales on the cheek 

 in a narrowish band. The length of the posterior hrab of the prse- 

 operculum is considerably less than that of the lower. Pectoral 

 terminating at some distance from the vent. The distance between 

 dorsal and caudal fins is more than the length of the base of the 

 former. 



Lake Titicaca. 



a. Three inches and a third long. From Mr. Pentland's Collection. 



11. JENYNSIA. 



Lebias, sp., Jemjns, 



Cleft of the mouth small, developed laterally and horizontally ; 

 ^ffiandible short, with the bones firmly united. Snout not produced. 

 Both jaws with a series of tricuspid teeth of moderate size. Scales 

 of moderate size. The origin of the anal fin is, in both sexes, be- 

 hind that of the dorsal, although the anal of the male is modified 

 into an intromittent organ, in which scarcely any of the rays remain 

 distinct, intestinal tract but slightly convoluted. 



E,io Plata. 



Although Mr. Darwin's Collection contained males as well as 

 females, Mr. Jenjais omitted to mention the former, probably consi- 

 dering the anal appendage to be an accidental mutilation of the fin. 



1. Jenynsia lineata. 



Labias lineata, Jemjns, Voy. lieayle, Fish. p. 116, pi. 22. fig. 2. 

 D. 9. A. 9. V. 6. L.lat. 30. L.transv. 8. 

 The height of the body is one-fifth of the total length (with the 

 caudal) , the length of the head two-ninths. Head depressed ; snout 

 obtuse ; mouth small ; upper jaw very protractile ; the lower one 

 rather the longer. Diameter of the eye two-sevenths of the length 

 of the head. The origin of the dorsal fin corresponds exactly to the 

 middle of the total length, and is somewhat in advance of that of the 



