FOSSIL FISHES. 619 



In general outline the} r correspond. The caudal fins are better preserved 

 but do not apparently differ in any essential feature. The ventral and 

 anal fins' are not preserved. The single specimen yet found shows the 

 dorsal aspect and the shagreen coating differs little if at all from that of 

 the other species. The pectoral fins are also of the same form as in those 

 but contain about twenty rays. 



But the fossil measures sixty-three inches in length, in spite of some 

 slight imperfection at the hinder end, and its teeth which are remarkably 

 well preserved and have been exposed with great care and skill, show 

 none of the usual cladodont features in the presence of lateral denticles. 

 For these reasons I am induced to separate this large form from the others 

 genericalry and yet to indicate its relationship by adopting the name 

 Monocladodus, in allusion to its single coronal tooth, which is shown in 

 Plate XL, fig. 2. 



The tooth consists of a single flattened pointed medial cusp, slightly 

 striated below and forking near the base which does not outwardly ex- 

 tend beyond the front of the cusp, but inwardly widens out so far as to 

 form a spreading surface of attachment to the skin of the jaw. In tront 

 view the general form is strikingly suggestive of Lamna, but the resem- 

 blance disappears on close examination. The striation is strictly confined 

 to the lower part of the cusp and does not consist merely of a longitudi- 

 nal roughening or of a faintly visible line-marking as in G. Kep J eri, but of 

 distinct and tangible unevennesses of the surface. The front face is 

 nearly flat, the hinder convex or doubly sloping 



Perhaps the most remarkable peculiarity of these teeth lies in the 

 fact that toward the back of the jaw they stand in pairs as shown in the 

 figure, one being close outside of the other. The outer one is frequently 

 broken, but this has evidently been done during fossilization or in the 

 extraction of the specimen from its refractory matrix. At least four of 

 the eight teeth remaining in position in the left mandible show this 

 character and more than one on the right side is also double. It is there- 

 fore not an accidental circumstance. Moreover in the front part of the 

 jaw two at least of the teeth show at their bases, outside, what are ap- 

 parently the points of others that scarcely rise above the base of those 

 in front of them. These cannot be young teeth, for the young teeth in 

 the sharks grow inside and behind those outside them which show signs 

 of use and wear that are not visible on these. If the outer teeth are 

 really in the act of being shed they would scarcely present the appear- 

 ance shown by those in the front of the mouth though this interpreta- 

 tion might be accepted regarding those near the back of the jaw. 



I propose to give to this fish the name UTonociadodus Clarki. It was 

 found in the Cleveland Shale in Cuyahoga county, Ohio, by Dr. W. 

 Clark. 



