1887.] FOSSIL CHLAMYDOSELACHUS. 543 



confirmed his opinion at greater length, and stated that the recent 

 fish should be named Didijmorlus aiic/uineus. Prof. Th. Gill was dis- 

 posed to consider Chlamijdoselachus to stand " nearer the true fishes 

 than do the Sharks proper, not because it appears to be in the line 

 of descent between the two, but because it is nearer the primitive 

 line from which both types have diverged." Thus far he agrees with 

 Mr. Garman, but he dissents emphatically from him in regarding 

 the recent acquisition as a Cladodont Shark, and agrees with Prof. 

 Cope that Chlami/dose/ackushad a representative in the Carboniferous 

 genus Diplodus or Diflymodus, although he does not think that the 

 two can be congeneric. He suggests the name Pteniodonta as pre- 

 ferable to the one given by Mr. Garman. A month later, however, 

 Prof. Gill withdrew his adliesion to the Diplodus scheme of affinity ; 

 and he says, " I am convinced not only that Didymodus has no 

 generic or even family relations with Chlamydoselachus, but that it 

 represents even a different order." His objection is founded on the 

 undoubted relationship of Diplodus and Pleuracanthus, and the 

 possession by the former of a large dorsal fin and nuchal spine, of 

 which there is no evidence in the recent fish ; and he concludes that 

 the anatomy of the latter will probably reveal a structure most like 

 that of the Notidanidas, but of a somewhat more primitive type. In 

 ' Science,' May 30th, 1884, Prof. Cope discusses the relationship 

 of Diplodus, Agass., and Didymodus, Cope, and regarding the former 

 as the teeth of the fish bearing Pleuracanthus-s^mes, states that it 

 must be separated from the genus Didymodus, and that Chlamy- 

 doselachus is distinct on account of the different structure of the 

 dorsal fin and the absence of a spine ; but that hitherto no Pleui'a- 

 canthoid spines have been found directly associated with Didymodus 

 (though they are found in the same strata), and consequently, so far 

 as we know Chlamydoselachus, it will not differ from Didymodus. 

 These views were published in greater detail in the July ' Proceedings 

 of the American Philosophical Society of Philadelphia.' And so 

 matters remained until t!ie following September, when Mr. Garman 

 read a paper at a meeting of the American Association for the 

 Advancement of Science, in which he strongly reiterated his views 

 as to its relationship with the fossil Cladodus, with the result that 

 both Profs. Cope and Gill abandoned their positions and accepted 

 the views of Mr. Garman, Prof. Gill still dissenting " from the opinion 

 that the Cladodontidfc are related to the Chlamydoselachidae rather 

 than the Hybodontid?e." In July 1885 Mr. Garman published a 

 detailed description of the fish in the ' Bull, of the Museum of 

 Comparative Zoology at Harvard College,' vol. xii. no. 1, pp. 1-35, 

 pis. i.-xx., in which he styles it " a living species of Cladodont 

 Shark." 



Leaving this extremely problematical relationship of Chlamydose- 

 lachus to be substantiated or otherwise by future investigation, it is 

 extremely interesting to find that ten years ago a fossil representative 

 of Chlamydoselachus was actually discovered and figured by the late 

 Robert Lawley. The specimen is from the Pliocene beds of Orciano 

 in Tuscany, and is described as very rare ; the teeth figured are 



3C* 



