GREGORY: FISH SKULLS 193 



In the cyprinid Jspius rapax, which lives on small fishes, the typical carp mouth has 

 been modified toward predatory habits. According to Thilo (1920, p. 221), the jaws are 

 now much larger, with sharp cutting edges; on the anterior end of the mandible is a sharp 

 tip, which fits into a corresponding excision of the upper jaw. The ascending process of 

 the dentary is further back toward the fulcrum and the long premaxillae exclude the maxillae 

 from the border of the mouth. Nevertheless, Thilo's description shows that the mechanism 

 as a whole is the same as that in the typical carp and the conditions in Aspius plainly 

 represent only a convergence toward the moderately protrusile jaws of the percoid fishes. 



From the evidence reviewed by Sagemehl (1891) it seems probable that the most 

 primitive members of the cyprinoid group are not the free-swimming types, with large 

 mouths, but the more sedentary or slow-moving, bottom-living forms, derived eventually 

 perhaps from some small-mouthed characin like Distichodus, which developed thick lips 

 and became edentulous. 



The absence of teeth on the jaws of cyprinoids is more than compensated by the 

 presence of tooth-like processes on the fifth ceratobranchials or lower pharyngeals, arranged 

 in one to three rows in different subfamilies. These teeth, being drawn upward by the 

 powerful action of muscles that are attached to the lateral fossa of the cranium, oppose a 

 prominent horny pad which rests on a raised bony projection from the basioccipital. Of 

 these pharyngeal teeth, Boulenger writes that "adapted to various requirements, [they] 

 may be conical, hooked, spoon-shaped, molariform, etc." 



In the suckers (Catostomidas), writes Tate Regan (1929, p. 315), "the premaxillaries 

 are small, the lips fleshy, the pharyngeal teeth in a single series often numerous, and the 

 pharyngeal processes of the basioccipital united to form an expanded perforated lamella, 

 rolled up at the edges and not covered by a horny sheath." These fishes feed on small 

 aquatic animals, weeds and mud. 



A median interparietal fontanelle of varying size and anteroposterior extent is found 

 in various genera of the different subfamilies of the cyprinoid group. Sagemehl (1891, p. 

 506) was unable to find any physiologic significance in this variable feature. He could 

 not accept E. H. Weber's suggestion that this fontanelle might afford access of sound waves 

 to the labyrinth, for the reason that it is always closed by a thick, fatty membrane, and 

 that between it and the nearest parts of the labyrinth lies a considerable mass of fatty inter- 

 dural tissue. On account of the presence of a similar interparietal fontanelle in certain 

 characins, and of its sporadic occurrence in the cyprinids, Sagemehl (1891, p. 495) was 

 inclined to regard it as an ancient hereditary or reversional feature of the whole cyprinoid 

 stem. In conclusion, Sagemehl (1891, pp. 580-594) has abundantly shown that the 

 cyprinoid skull as a whole gives evidence of derivation from characinid ancestors; but I 

 cannot accept his conclusion that such resemblances as there may be between the skulls 

 of cyprinoids and characins and that of Amia are indicative of the derivation of the former 

 two from the latter. 



The extraordinary idea expressed by Garstang (1932) that the presence of an adipose 

 fin in various Ostariophysi, Isospondyli and Iniomi compels us to carry the Teleostei back 

 to osteolepid-like ancestors, finds no support, I think, in the study of their skull structure. 



The otoliths of the cyprinoid families aflPord some interesting evidence as to relation- 

 ship. In the Cyprinidae, according to Frost (1925^, p. 561), the otoliths of Barilius "present 

 certain Characid features. They are very flat compared with those of the remainder of 



