Fishes of the Order Cyprinodontes 23 



of 9 rays, the third to the fifth being prolonged to form a short lobe, render- 

 ing the edge of the fin strongly falcate; these are the same rays which in the 

 male are much more produced to form the gonopodium; the origin of the 

 anal is midway between the base of caudal and a point behind the eye equal 

 to half or all its diameter. The paired fins are broadly rounded and short, 

 the pectoral being about as long as the postrostral length of the head, the 

 ventrals reaching only two-thirds the distance to the anus or to the origin 

 of the anal fin. 



The male, as mentioned before, is much smaller than the female. Its 

 body, while actually not deeper, appears to be so, as the back is more strongly 

 arched; the body is decidedly more compressed; the width of the head is 

 contained about 1.6 times in its length. The proportions are like those of the 

 young females, or like the adult females of amiectcns proper. The coloration 

 and color range agree with those of the female. The dorsal fin is inserted 

 midway between the base of the caudal and the anterior half of the postorbital 

 length of the head; the origin of the anal midway between base of caudal 

 and tip of mandible; the ventral fins extend to the origin of the anal. 



The gonopodium (intromittent organ) is elongate, reaching when 

 depressed nearly to the lower procurrent rays of the caudal fin. Its finer 

 structure is like that of annectens proper. The organ is developed from the 

 third, fourth, and fifth anal rays when the fish has reached a length of about 

 20 mm. to caudal. Over one hundred males were examined with the organ 

 developed; in length these specimens vary from 21 to 49 mm., few l^eing 

 more than 30 mm. long, and only the largest being longer than 36 mm. In 

 the specimens from 21 to 36 mm. long the serrae-bearing segments of the 

 second produced ray vary in number from 8 to 12, averaging fewer in the 

 smaller specimens than in the larger ones; in the largest male (49 mm. long) 

 the number is increased to at least 18. The number of serrae doubtless 

 increases with age, as might well be expected, for one serra is developed 

 from each of the distal articulations of the ray, and the number of articula- 

 tions, of course, increases with age. 



EXPLANATION OF FIGURES 



All of the figures are of gonopodia, the intromittent organ formed by the modi- 

 fication of rays 3, 4 and 5 of the anal fin in the male. In each figure the rays are 

 numbered, and if divided the anterior (a), median (m) and posterior (p) branches 

 of each ray are lettered as indicated; further, the left (1) and right (r) halves of 

 certain branches are also shown, and so lettered. The gonopodia are all shown 

 as semitransparent objects, and all, with the exception of that of PocciHopsis liit::i 

 (figure 3) are viewed from the left side. All the figures were drawn with the aid 

 of a projection machine in order to secure accuracy of proportions; detailed correc- 

 tions of the outlines of individual segments were made while the object was being 

 examined under a^ high power of the microscope. 



