The T^atural History of the Frilled Shark 



309 



Text-figure 27 



Teeth of Cladodus (Xl?): A, of C. mira- 



bill's Ag. ; B, of C. acutus Ag. Note lengths 



of secondary cusps and striations on all 



cusps. 



After Agassiz, 1S43. 



ones but lower than the central cusp. Furthermore the enamel of all cusps, main and 

 lateral, is grooved or striated, in strong contrast to the smooth enamel of the teeth of 

 Chlamydoselachus. 



It seems to us that while the teeth of Cladodus are constructed on the same funda- 

 mental plan as those of Chlamydoselachus, they are much more primitive and more like 

 dermal denticles (Text'figures 13 and 17). This is 

 evident in the stoutness of all the spines, the lesser 

 development of the outer lateral spines, the retention 

 of the fluting of the surface, and the lesser degree of 

 development of the enamel. 



In the paper just referred to, Garman (1885.2) 

 passed some strictures on Cope's article (synopsised 

 on our p. 307) dealing with the skull of Didymodus. 

 So in the American ?iaturalist for September 1885 

 (pp. 878-879), Cope complained strongly that Gar- 

 man had made such comments, saying in reply: 

 "The surprise which these criticisms occasion in- 

 creases when it is understood that they are derived 'from a study of the illustrations' 

 [of the teeth of Didymodus] and not of the specimens themselves." In fairness it 

 must be noted that all Cope's pronouncements on the affinities of Chlamydoselachus were 

 based solely on Carman's drawings published in Bulletiyi Essex Institute, Jan. 17, and in 

 Science, Feb. 1, 1884, and reproduced herein as Text'figure 1 in the exact sisje in which 

 they appeared in Science. Possibly, however, he had later seen Carman's more complete 

 drawings (1885.2, July) of the fish, its teeth, and its various organs. Furthermore in this 

 same note (1885, p. 879), Cope complained that Garman alleged that he (Cope) had re- 

 placed the name C. anguineus by Didyynodus anguineus, and stated positively that ''I 

 have never proposed or used this name at the places cited, or elsewhere." However, he 

 evidently forgot that he had stated (American 7<laturalist, April, 1884, p. 413) that the 

 name C. anguineus could not stand and that ''The species then should be called Didymo- 

 dus anguineus.'" 



This controversy was reviewed by J. W. Davis, the eminent English paleichthy- 

 ologist, whose experience fitted him admirably to pass on the merits of the question. After 

 comparing the structures of Pleuracanthus { = Diplodus = Didymodus) and Chlamy- 

 doselachus and finding them very different, Davis (1885) concluded that ''The resemblance 

 of the teeth as first insisted upon by Professor Cope is only a superficial one and rests 

 simply on the accidental circumstance of each having three denticles." 



To make matters still clearer we are reproducing from Davis' paper on the Pleura- 

 canthidae,^ his drawings of fiwe teeth of Pleuracmit/ius laevissimus Ag. { = Diplodus gib- 

 hosus Ag.) in natural sizie (Text-figure 28). These show considerable variation in form 



' Davis, J. W. On the fossil fish remains of the Coal Measures of the British Isles. Part I, Pleuracanthidae. Sci. Trans. Roy. 

 Dublin Soc, 1892, 2. set. 4 (Pleuracanthus laevissimus Ag. = Diflodus gibbosus Ag., p. 726, pi. LXV, figs. 5, 7, 11, 13, 15). 



