304 0. P. Hay — Species of Saurocephalus. 



It has been supposed that the foramina, situated one opposite 

 each tooth and on the mesial face of the maxilla and of the 

 dentary, are for the transmission of nerves and vessels to the 

 teeth. Kichard Owen* seems not to have so regarded these 

 foramina. He believed that they " lead to the cavities contain- 

 ing the germs of the successional teeth." The latter probably 

 began their development in, or at the bottom of, these foramina ; 

 but they soon passed more deeply into the bone. In fig. 1 at t 

 there is found a developing tooth whose tip is on a level with 

 the row of foramina ; but its root extends high up into the 

 bone. Nerves and vessels entering the tooth by way of the 

 foramina alluded to would have to take a very tortuous course. 

 The functional tooth immediately below the young tooth fig- 

 ured seems already to have suffered some reduction of its fang. 



The germs of the teeth of the /Saurocephalidce did not gain 

 a lodgment in the bones of the jaws in the same way that the 

 teeth of the higher vertebrates did. In the latter the fangs 

 were first planted in grooves in the dental borders of the bones ; 

 and we must suppose that these grooves, at first shallow, have, 

 in successive generations, deepened and become portioned off 

 to form sockets. In the Saurocephalidce the teeth, developing 

 originally on the dental border, have gradually migrated away 

 from this border, on the mesial face of the supporting bones, 

 and, by means of the foramina described above, have made 

 their way through the mesial wall of the sockets. The notches 

 found in the species referred to Saurodon show the earliest 

 stages of this migration. 



The distinguished palseo-ichthyologist, Mr. A. S. Woodward, 

 has recently kindly called my attention to a suggestion made 

 by Prof. E. D. Cope that the Saurocephalidce are closely 

 related to the Chirocentridce, represented by the large Chiro- 

 centrus dorab of the Chinese and Indian seas. I have unfortu- 

 nately had no opportunity to study a skeleton of this fish ; but, 

 judging from the figures of the fish found in Cuvier and 

 Valenciennes, pi. 565, and in Day's Fishes of India, pi. clxvi, 

 fig. 3, its external appearance must be much like that of the 

 extinct Xiphactinus. Nevertheless, we have no intimations 

 that the teeth of Chirocentrus are fixed to the jaws in any way 

 different from those of ordinary fishes. The fixation of the 

 teeth in sockets is an unusual thing among fishes ; and this 

 character alone, it appears to me, is sufficient to remove 

 Xiphactinus and its allies from the Chirocentridse, although 

 not necessarily to a great distance. I suspect that the Sauro- 

 cephalidce will, when they are better known, show distinctive 

 characters in the vertebral column also. 



* Odontography, p. 131. 



