OCR Text |
Show 1 9 0 6 .] SELACHIAN FISHES. 7 5 5 In all the members of this family the teeth are small and obtuse. There is a more or less distinct longitudinal fold on each side of the tail. The differences in the shape of the body and the development of the pectoral fins are considerable, but from anatomical considerations there can be no question that we are here dealing with a very natural group. Discobatus, in which the pectoral fins extend as far forward as in Raia, resembles Rhinobatus in the arrangement of the cartilages of the dorsal fin and in the shape of the ventrals, and should not be placed in the Raiidse. The number of radials directly attached to the pectoral arch varies from none in Sclerorhynchus and one in Pristis to eight in Trygonorhina. Family 2. R aiidje. Prseorbital cartilages articulated to the propterygia. Usually two small dorsal fins near the extremity of the tail; caudal fin Text-fig. 124. b, basals ; r, radials. small oi absent, pectorals extending to the snout, sometimes confluent anteriorly ; pelvics notched. Basalia of the dorsal fin directed obliquely upwards and backwards, anteriorly imbedded in the body, elsewhere connected by a membrane to the back of the tail; radialia nearly reaching the free edge of the fin, some |