FOSSIL FISHES. 45 



lance-shaped and serrated cornua, by its tuberculated base and by the 

 absence of a median denticle. 



Dijplodus compressxis (Fig. 2) is never more than lialf as large as D. 

 latus, and has relatively broad, serrated, flattened and divergent cornua. 

 These are often nearly straight, and sometimes have the sharpness of the 

 edges increased by a concavity of the slope from the median line. It 

 might be supposed that this v^'as only the immature state of D. latus, 

 which it somewhat resembles in form, but in that species the cornua are 

 more lance-shaped and the surfaces more uniformly arched. The tuber- 

 culated base and the absence of a median denticle are also characters 

 wanting in D. compressus. It may be said also that some thousands of 

 the teeth of the latter species have been found at Linton, so like in size 

 and shape that they evidently exhibit its normal features. From this 

 average character the teeth of D. latus depart very -widely. 



As has been elsewhere remarked the differences between D. comjjressus 

 and D. gracilis (Figs. 3, 3 a) are not strongly marked nor very constant, 

 and they may be but varieties of the same species. The figures now pub- 

 lished will show that the teeth named D. gracilis are nariower, with less 

 spreading, more curved, and less flattened cornua, than those to which the 

 name D. comjyressus has been given. There are, however, among the 

 specimens from Linton, some teeth which seem to share the characters 

 of the two species, and it may be found that they I'un into eai-h other. 

 Several jaws have been obtained at Linton to which the teeth of Diplodtis 

 are still attached. These have been carefully examined in order to ascer- 

 tain what diversity of form could be observed in the dental series of one 

 individual, but they are too imperfect to fully settle this question. The 

 upper and lower jaws have not yet been found together, and although 

 there seems to be less variation of size and form than was expected in 

 the teeth of a single jaw, the teeth of the upper and lower jaws may 

 have been somewhat different. It will be necessary to liave the entire 

 dentition under view before the limits of variation in the teeth can be 

 accurately defined. 



Cladodus acuminatus, Newb. 



Plate LVni., Fig. 4. 



Cladodus acuminatum N.; Proc. Pbila. Acad. Nat. Sciences, 1856, p 99. 



Teeth of medium size, average specimens being about one inch in height, 

 and three-fourths of an inch in breadth of base ; central denticle robust, 

 conical and very acute, with a nearly circular section throughout, both 



