250 THE PLAGIOSTOMIA. 



of the family. Some of them, as Rhina alifera Minister, do not differ greatly 

 from recent species; others, as Rhina speciosa Meyer, have bodies that are more 

 slender and tails that are longer, thus approaching more closely the shape of most 

 living sharks. 



Rhina. 



Rhina (Aristotle) Klein, 1742, Hist, pise, miss., 3, p. 13; 1776, Neuer schaupl., 2, p. 587; Walbaum, 



1792, Artedi, p. 580; Rafinesque, 1810, Caratteri, p. 14; Ind. itt. Sic, p. 45. 

 Squatina Yalmont, 176S, Diet, d'hist. nat., 1, p. 117; Dumeril, 1806, Zool. anal., p. 102. 



Body, head, and tail depressed and flattened. Head short, broad; mouth 

 wide, anterior; nostrils anterior; a thin fold along each side from the nostril to 

 the angle of the jaws; one labial fold on the upper jaw, two on the lower. Eyes 

 small, superior; eyeball free from the edge of the orbit. Spiracles behind the 

 eyes. Gill openings five, lateral, crowded together, in front of the pectoral. 

 Pectorals broad, extended forward, free from the head. Dorsals small, on the 

 tail, not preceded by spines. No anal fin. Caudal axis not raised; supracaudal 

 fin shorter, more erect; subcaudal widening backward. Three strong labial 

 cartilages, joined, to form the angle of the mouth, at a distance from the angle 

 of the jaws. Anterior nasal valve with two cirri and more or less fringed in the 

 young. Pterygoquadrate with a long flexible process through the orbital region 

 and the top of the skull. Hyomandibular and branchial cartilages strong, 

 flattened. Pelvis curved backward in the middle and with a short process 

 extended forward from each end, as in the Rhinobatidae and some other Batoids. 

 A blunt keel on each side of the tail, posteriorly. 



The species differ in regard to the pterygoquadrate process: — in R. squatina 

 the postorbital process unites with the skull in front of the foramen, thus com- 

 pleting the latter, but in R. philippi and R. calif oniica there is no such union 

 and the foramen remains open toward the orbit. 



Because of individual variations in the tubercles of the back, in the point of 

 origin of the first dorsal in relation to the extremities of the ventral fins, and in 

 the fringes of the nasal valves, they have not been used in distinguishing the 

 species. Dependence has been placed rather on the shape of the caudal fin, the 

 angle formed by the meeting of a line along the outer edge of the pectoral with 

 another across the hind margin of that fin, the condition of the fold along the 

 side of the head, and the completeness of the foramina for the processes of the 

 pterygoquadrates in the top of the skull. 



Temperate and tropical seas. 



