4 MEMOIRS OF THE CARNEGIE MUSEUM. 



teeth of the maxillary are similar to those of the premaxillary and the lateral teeth 

 of the mandible are always smaller than those near the front. A frontal and a 

 parietal fontanel are present, the latter being the larger, truncated in front; the 

 former is triangular, the base of the triangle being caudad. The occipital crest is 

 narrowly triangular and divides the scales of the two sides for a distance of about 

 one-fourth of the length from its base to the dorsal. The dorsal is short, pointed, 

 consisting of one rudimentary and ten developed rays; having its origin midway 

 between the tip of the snout and the base of the middle caudal rays. The adipose 

 is a small free lobe as in the greater number of all the characid fishes, and is placed 

 over the end of the anal. The caudal is deeply forked. The anal is emarginate, 

 having its origin under the last dorsal ray, and it consists of twenty-five rays. The 

 ventrals are placed slightly in front of the origin of the dorsal and they do not quite 

 reach the anal. The pectorals are lanceolate and do not quite reach the origin 

 of the ventrals. The scales are thin, very regularly arranged. The fins are naked 

 except for a few scales along the base of the anterior anal rays. There is a well- 

 developed axillary scale over the ventrals. There are thirty-five scales along a 

 median series, eight of which have lateral line pores. There is a dark spot on the 

 sides from about the third to the fifth scales of the lateral line, and another larger 

 spot on the end of the caudal peduncle and the base of the caudal. In a triangular 

 area over the sides of the anterior air-bladder the wall of the body consists of skin 

 and peritoneum only. 



Minor deviations from the generalized type. — The deviations from this general 

 type are numerous, but not very great. The greatest deviations are found in the 

 size of the frontal fontanel; the armature of the cheek, especially the postorbital 

 portion of it; the length of the anal; the degree of the development of the pseudo- 

 tympanum; and especially the size of the mouth and its parts and the style of the 

 teeth. Leaving these to be considered last, we find some of the species (Aphyo- 

 charax) are much less compressed than others, and in these the depth is frequently 

 less than one-third of the length, the minimum depth being contained about four 

 times in the length in a number of species of Aphyocharax. In the deepest the 

 depth is contained but 2.4 times in the length {Megalamphodus megalopterus) . 

 The head varies from 3.3-4.66 in the length in different species. It is comparatively 

 shortest in Paragoniates paixiguayensis and comparatively longest in Spintherobolus. 

 The eye is always large. In different species it is contained from 2.3-4.33 in the 

 length of the head, but in only two forms, Grundulus and Spintherobolus is it con- 

 tained as many as 3.75 times. In the great majority of cases it is contained 2.5-3 

 times. The adipose fin is absent in Grundulus and Spintherobolus, which otherwise 



