114 ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 



reach, according to Valenciennes, to the gill-opening, if not beyond it, here 

 only attain to beneath the middle of the eye ; and this character is invariable in five 

 specimens which Mr. Darwin has brought home. Judging from the description, 

 there would seem to be one or two further differences : the profile appears to be 

 more rectilineal, the pectoral spine shorter, and smoother on its external margin. 

 The colours are on the whole similar, but the pectorals and ventrals darker : the 

 latter, which are said to be yellow in the C. punclatus, are here quite dusky in 

 every one of the specimens. 



The exact locality in South America in which Mr. Darwin obtained this 

 species is uncertain, as the specimens have lost their attached labels. 



Family.— CYPRINID^. 



1. PoZCILIA UNIMACULATA. Val. 



Poecilia unimaculata, Val. in Humb. Zool. et Anat. Comp. vol. ii. p. 158. pi. 51. fig. 2. 

 Form. — Body oval, slightly elongated, thick anteriorly, compressed behind. The dorsal and 

 ventral lines meeting at the mouth at an acute angle ; but the head, when viewed from above, 

 broad, and very much flattened between the eyes, and the snout obtuse. Greatest depth 

 about one-fourth of the entire length : thickness two-thirds of the depth. Length of the head 

 nearly equalling, or a little less than, the depth of the body. Mouth small : jaws very pro- 

 tractile ; each with a single row of very fine, close-set, pointed teeth ; the lower one a trifle the 

 longest. Eyes large, their diameter three and a half times in the length of the head, high in 

 the cheeks, reaching to the line of the profile. Nostrils consisting of one small orifice a little 

 above and rather in advance of the eyes. 



Scales large, investing the head and all the pieces of the gill-cover, though very thin and 

 transparent on the opercle and not very obvious there. On the body there are about eight in 

 the depth, and twenty-seven or twenty-eight in a longitudinal row from the gill-opening to the 

 caudal. One taken from the middle of the side found to be of a semi-elliptic form, the exposed 

 portion marked with numerous very fine curved concentric lines, the basal with sixteen or 

 seventeen deeper-cut nearly parallel striae gradually lengthening from the sides towards the 

 middle, but not converging to a fan. Lateral line very faintly marked out by a dotted line, 

 scarcely obvious in some places. 



Dorsal small, commencing exactly at the middle point of the entire length, measuring this 

 last quite to the extremity of the caudal. Anal similar and opposite ; in strictness, however, 

 terminating a very little in advance. The last ray in both these fins double : the first two in 

 the anal short. Caudal rounded. Pectorals and ventrals small and narrow, the former three- 

 fourths the length of the head ; the latter not above half the same. The pectorals, when laid 

 back, reach to the insertion of the ventrals, but the ventrals hardly reach to the commencement 

 of the anal. 



B. 5 ; D. 7 ; A. 9 ; C. about 24, including short ones ; P. 14 or 15 ; V. 6. 



Length 2 inches. 



