66 



PROCEEDINGS OP THE AMERICAN ACADEMY 



has its lower division two-lobed, the lower lobe looking like a 

 second anal fin. The specimen, which he thought full-grown, 

 was about one foot and a half long. The teeth in front differ 

 much from those on the sides and back of the mouth ; they 

 are quite "small in front, gradually becoming larger, and then 

 again smaller ; the anterior teeth are trilobed ; the lobes grad- 

 ually diminish backwards, become flat, and then rounded on 

 their upper surface ; there is a ridge on the median line, the 

 remains of the three cusps. In the New Holland species, the 

 front teeth have the median cusp much the longest, the back 

 teeth being much the broadest. 



Professor Agassiz compared these teeth with the fossil teeth 

 he had received from Indiana. The teeth of the genus Psam- 

 modus resemble the back teeth of Cestracion, and are marked 

 by numerous minute points ; those of the genus Strophodus 

 resemble Cestracion, having also a central prominence ; in the 

 genus Ozodus, the teeth are undulated, like the second form 

 in Cestracio7i, but with lines radiating from each of the three 

 cusps; in the genus Helodus (perhaps to be suppressed) the 

 teeth have a prominent tubercle, like the anterior teeth of 

 Psammodus ; another reason for suppressing the former genus 

 is that it is always found with the latter ; in the genus Peta- 

 lodus the teeth are much compressed and spreading, with a 

 narrow root. 



These are the same genera as are found in Europe ; the 

 specific identity he had not as yet determined. Other Euro- 

 pean sharks having no living representatives are also found 

 here. The genus Ctenoptychius, the whole margin of whose 

 teeth is serrated ; the genus Hybodus, with cylindrical teeth, 

 longitudinally striated, like those of Saurians, from the folds 

 of the enamel ; the genus Dendrocladus, having large dorsal 

 spines, sometimes two feet long, which are always found with 

 the teeth. Speaking of the gigantic species which must have 

 borne these spines, he remarked that it was neither the first 

 nor the last created members of any class in the animal king- 

 dom which were the giants of that class ; but rather those 

 created at the middle epochs. 



