1906.] SELACHIAX FISHES. 751 



has shown that it is closely related to Squalas. The anatomy of 

 Pristis has been described by Gegenbaur and agrees in all essential 

 features with that of Rhinohattts. In spite of these researches the 

 writers of modern text-books still seem to believe in some special 

 relationship between these two genera, which resemble each other 

 to a certain extent in the appearance of the saw-like rostrum, but 

 difler so widely in other respects. 



Family 5. Squatinid^e. 



Body depressed. Five gill-clefts on each side, the last in front 

 of the base of the pectoral, which is produced forward external to 

 the gill-clefts, this anterior extension being fi'ee from the body. 

 Dorsal fins without spines, situated on the tail ; anal fin wanting. 

 Teeth subconical, pointed. Pterygo-quadrate not articulated to 

 the cranium, Yei'tebral centra calcified. 



The remarkable genus Squatina, dating from Jurassic and 

 Cretaceous times, is unquestionably related to the Squalidse. It 

 has been regarded as a connecting-link between the Sharks and 

 Rays, but in the strongly depressed form of the body and the 

 backward shifting of the dorsal fins it has gone further than the 

 more primitive of the true Batoids, yet without modification of 

 pterygo-quadrate, hyomandibular, hyoid or pectoral arch fi-om the 

 Squaloid type. The gill-clefts are lateral in position and crowded 

 together. The arrangement of the cartilages of the pectoral fin 

 is far more similar to that found in the SquaHdse than to that of 

 the Batoids. The cartilaginous supports of the dorsal fin are 

 arranged as in the Squalidse. The paired praeorbital cartilages 

 typical of the Batoidei are absent. 



In favour of Batoid relationships may be cited the calcification 

 of the vertebral column, which is rather similar to that of the 

 Rhinobatidfe, and the structure of the mixopterygia, which, 

 although extremely similar to those of /S'5'^taZ^ts, present two features 

 characteristic of the Batoids, viz. the development of a ventral 

 covering piece and the presence of a special glandular body in the 

 glandular sac. 



To sum up then : — In all essential characters, i. e. position of 

 the gill-clefts, structure of pterygo-quadrate, hyomandibular, hyoid 

 and pectoral arch, arrangement of the cartilaginous supports of 

 the pectoral fin, Squatina is a typical Sqiboloid. In these and other 

 features it shows specially close relationship to the Sqvialidse. The 

 depressed body, the extension forward of the pectoral fins, and 

 the backward position of the dorsal fins are Ray-like features of 

 specialisation which do not, however, appear to indicate Batoid 

 relationships. Finally, the structure of the vertebral column and 

 the mixopterygia point to real affinity to the Hypotremata, and 

 we must infer that both they and Squatina have evolved from 

 Sharks similar to the Squalidse, but in which probably the 

 vertebral column and the mixopterygia had already attained a 

 structure somewhat similar to that found in Squatina. 

 Piioc. ZooL. See— 1906, No. L. 50 



