ORDER TELEOSTEI. 997 



has the same distribution as the genus, are very common in the 

 coprolitic beds of the Cambridge Greensand, and were for a long 

 time referred to the American Saurocephahis lanciformis, which was 

 once thought to be a Reptile. These teeth are compressed, and 

 without marginal serrations. The fins were provided with large 

 ribbed spines, which were at one time referred to the Selachian 

 genus Ptychodus, and subsequently were made the type of another 

 genus under the name of Pelecopterns. 



Family Dercetid^ (Hoplopleurid^e). — The members of the 

 second family of Saurodonts are characterised by their elongated 

 shape, their powerful dentition, and the presence of several series 

 of large triangular scutes along the sides of the body ; there is 

 but one dorsal fin in those forms in which the fins are known ; 

 the teeth are not implanted in sockets ; and the skull is frequently 

 produced into a rostrum. This family probably passes impercep- 

 tibly into the next. 



The typical genus Dercetis (in which Leptotrachelus may be in- 

 cluded) occurs in the Chalk of England, Bohemia, and the Lebanon, 

 and also in the Upper Cretaceous of Westphalia ; it is characterised 

 by the length of the upper jaw exceeding that of the lower, and by 

 the presence of five rows of scutes, of which the middle one bears 

 the lateral line. The allied Aspidopleurus is confined to the Lebanon 

 beds. Other members of this family are Blochius, from the Middle 

 Eocene of Monte Bolca ; Plinthophorus, of the English Chalk ; 

 Pelagorhynchns, from the Upper Cretaceous of Westphalia ; and 

 Saiirorhamphus, from that of Istria. Plinthophorus has two rows of 

 scutes, but is otherwise naked. 



Family Enchodontid^e. — The genera which may be provision- 

 ally grouped under this name are distinguished by the moderate 

 lateral compression of the body, which may be either naked or 



Fig. 936. — Skeleton of Eurypholis Boissieri ; from the Chalk of the Lebanon. 

 Reduced. (After Pictet and Humbert.) 



covered with scutes, and by the elongated premaxillae and maxillae, 

 which carry small teeth anchylosed (like those of the mandible) to 

 the bone. A considerable portion of the maxilla is excluded from 

 the margin of the jaw by the premaxilla ; teeth occur on the pala- 



