2844 



THE BONY FISHES AND GANOIDS 



HEAD OF A FOSSIL CYPRINODONT, WITH 

 ONE OF THE SCALES ENLARGED. 



viviparous; and the males, which are much inferior in size to the females, and, 

 according to Dr. Giinther, probably the smallest living fishes, frequently have the 

 anal fin specially modified to aid in the reproductive process. As a rule, the fins 

 are relatively larger in the males than in the females, and there is likewise some 

 difference in the coloration of the two sexes. In a fossil state, remains of the 



typical genus occur in the Miocene strata of the 

 Continent, which have also yielded others re- 

 ferred to an existing American genus; while 

 the head of a species much larger than any now 

 living has been described from the Pliocene of 

 India, this specimen being figured in the accom- 

 panying illustration in order to show the scales 

 on the head so characteristic of the family. 

 Cyprinodonts are represented by about a score 

 of genera, which may be divided into two sub- 

 families, according to the nature of the food. 

 In the first of these, which includes the typical 

 genus Cyprinodon, and has a distribution co- 

 extensive with that of the family, all the forms 

 are carnivorous or insectivorous, and are char- 

 acterized by the firm union of the two branches 



of the lower jaw in front, and likewise by the shortness, or slight convolution 

 of the intestines. On the other hand, in the second subfamily, which is exclusively 

 restricted to tropical America, the species seek their food in mud, and have the 

 two branches of the lower jaw but loosely joined together, while the intestine is 

 highly convoluted. It is in this group that the sexual differences are most 

 strongly marked. 



As an example of the family we take a remarkable genus belonging 

 to the first subfamily, represented by three species from tropical 

 America, one of which (Anableps tetropthalmus) is shown in the following 

 illustration. Having a broad and depressed head, with the region over the eyes 

 much raised, the elongate body compressed in front and depressed behind, a pro- 

 tractile muzzle, and the cleft of the mouth horizontal and of moderate size, these 

 fish are specially characterized by the structure of the eye, which is quite unique 

 among vertebrates, and from which they derive their name. In each eye the 

 integuments are divided into an upper and a lower moiety by a dark-colored trans- 

 verse band in the outer layer; the pupil being likewise bisected in the same plane 

 by means of a lobe projecting from each side of the iris. The scales are of small or 

 moderate size; the dorsal and anal fins short, the latter being placed in advance of 

 the line of the former, and in the male (which in this genus is larger than the 

 female, modified into a long, thick, scaly organ, with an aperture at the end. 

 These fishes are the largest existing members of the whole family, growing nearly 

 to a foot in length. They are abundant in North Brazil and the Guianas, where 

 they frequent mud banks on the coast and in the estuaries of the larger rivers; 

 many of them being often left stranded by the retiring tide, where they progress 



Double Eyes 



