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TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



carried on the under surface of the basioccipital bone. In the tarpon this fossa, which 

 is likewise prominently developed, may also lodge some of the muscles of the branchial 

 apparatus. 



The most massively developed part of the entire cranium is the basioccipital, which 

 serves as a base for the converging lines of stresses from the rest of the skull. The cranial 

 base is further strengthened posteriorly by the incorporation of the first vertebra into the 

 occiput (Fig. 32^). 



Chirocentrids. — In the modern Elops and the tarpons the maxilla is overlapped at its 

 proximal end by a large mallet-like process of the palatine (Figs. 31, 33). This character 

 is emphasized in the existing Chirocentrus (Fig. 34) and in the Cretaceous Ichthyodectes 

 (Fig. 35), Portheus (Fig. 36) and allied genera. These are all referred by Woodward to the 

 family Chirocentridae (Saurodontidse), which he regards as being related on the one hand 

 to the older Leptolepidae and to the Clupeidse on the other. 



The skull of the modern Chirocentrus dorab (Fig. 34) has been shown by Ridewood 

 (1904Z), pp. 448^53, 491^92) to agree closely in many details with the clupeid type. 

 This again tends to strengthen the bonds between the Elopidae and the Clupeidae. It is 

 true that the teeth of the Cretaceous chirocentrids (saurodontids) are implanted in distinct 

 sockets in the bone, while those of the modern Chirocentrus are merely ankylosed to the 



scale h 



>one 



om 



rl Chirocentrus dorab 



Fig. 34. Chirocentrus dorab. After Ridewood. 



bone; but a similar difference separates the Cretaceous Pachyrhizodus from other genera 

 of the Elopidse (Woodward, 1901, p. 37). In Chirocentrus also this last feature may very 

 well be a specialization and it hardly outweighs the striking resemblances, noted by 

 Boulenger and Woodward, between Chirocentrus and the Cretaceous saurodonts. For 

 example, Woodward in his memoir "Fossil Fishes of the English Chalk" (Pt. II, 1903, 

 pp. 93-95) describes and figures the crania of Chirocentrus dorab and Ichthyodectes sp., 



