142 



PALEONTOLOGY 



The Pycnodonts so characterized are further distinguished 

 from the closely-resembling lepidoid genus DcqiediiLS, by having 

 the small anterior teeth conical and single-pointed, instead of 

 being bifurcate ; and although this character is subject to 

 occasional variations, nevertheless, on taking a comprehensive 

 view of all the dapedioid species, it seems to have been suffi- 

 ciently constant to warrant the continuance of the separation 

 of the group into the unicuspid and bicuspid species. And 

 Sir P. Egerton has accordingly proposed to apply the generic 

 terms jEchmodus (from aiyjin, a point, and odovg, a tooth)* for 

 the unicuspid and pycnodont species, formerly termed Tctra- 

 r/onolcjris, and to continue the name Dapcdius for the bicuspid 

 and unequivocally lepidoid homocercal deep-bodied Ganoids, 

 many beautiful species of which are found in the lias. 



Fig. 55. 

 Pycnodus rhomhus (Upper Oolite). 



Genus Pycnodus (fig. 55). — The type-genus of this sub- 

 order is characterized by the large size of the round flat 

 crowned teeth, which cover the broad jaws as by a pave- 

 ment of from three to five rows ;t at the fore-part of the 

 jaws are two or more trenchant incisive teeth both above and 



* Proceedings of the Geological Society, May 1854, p. 367. 

 f For the disposition of these teeth on the palate, see Owen's Odontography, 

 vol. i., pi. 34, figs. 1 and 2 ; and for their microscopic structure, ibid, p. 71, pi. 33. 



