260 THE PLAGIOSTOMIA. 



Pristidae. 



In this family the Platosomia make their nearest approach to the Antacea. 

 The elongate form and the comparative freedom of the head from the pectoral 

 fins give an appearance of nearness to the sharks that loses significance as it is 

 seen that in all essential features the Pristidae are more closely allied to the 

 skates. By some authors the family is included in the Rhinobatidae. In the 

 species of Pristis, now living, the body and tail are elongate, flattened on the 

 lower surfaces, and the snout is produced as a long flat blade, on each edge of 

 which is a series of strong teeth, supported by prolongation of the cartilages of 

 the skull in three to five more or less calcified tubes. The gill openings are below 

 the body. In the pectoral fins the propterygia are as well developed as the meta- 

 pterygia; the fins are united to the head opposite the gills but do not extend to 

 the snout. A single genus of half a dozen living species represents the family 

 in recent times. With it have been placed the fossil genera Propristis Dames, 

 1883, from the Lower Tertiary of Egypt, in which the rostral tooth-bearing mar- 

 gin is dermal, and Sclerorhynchus Woodward, 1S89, from the Upper Cretaceous 

 of Mt. Lebanon, Syria, which genus has swollen-based teeth, more like the tu- 

 bercles, on the edges of the rostral cartilages. Another genus of fossils, Ambly- 

 pristis Dames, 1888, founded upon broad short rostral teeth from the Egyptian 

 Eocene, is also said to belong here. 



That the Pristidae dwell upon the bottom is evident from the fins, the pave- 

 ment-like oral teeth, the size of the spiracle, the small gill openings, and the worn 

 condition of the scales on the lower surfaces. 



Pristis. 



Pristis Klein, 1742, Hist, pise, miss., 3, p. 12; 1749, ibid., 5, p. 78; 1779, Neuer schaupl., 7, p. 403. 



Rostral teeth firmly imbedded in the rostral cartilages, except in the very 

 young. Mouth transverse; oral teeth small, in pavement, smooth, in many 

 rows (70-178 or more) on the upper jaw. Edge of the orbit not free from the 

 eye in its upper half, the lower half of the orbit serving as a nictitating membrane 

 when the eye is retracted. Spiracles moderate, behind the eye. Gill openings 

 ventral. Pectorals united to the head along the gills, not continued to the 

 snout. Caudal axis slightly raised. Intestine with about eight turns in the 

 spiral valve. Pelvis convex in front, without lateral processes directed forward 

 from each end. 



