338 Prof. Morris — On the Genus jEchmodus. 



Species with a short dorsal fin, two rows of fulcra on all the fins, 

 [vertebral column completely ossified and terminated as in all the 

 homocercal Ganoids^] — Lepidotus. 



According to Prof. Huxley, in a note to his valuable Memoir, On 

 the Classification of the Devonian Fishes,^ the above genera belong 

 to the second sub-order, Lepidosteidce of the Ganoid fishes, and to 

 the family Lepidotini, which he distinguishes from the first sub- 

 order Lepidosteini, in having — the maxilla in one piece, branchi- 

 ostegous rays many and enamelled, the anterior ones taking the form 

 of broad plates, and he classes together as one of the sub-families, 

 JEchnodas, Tetragonolepis, Dapedius, Lepidotus, etc. 



The genus Tetragonolepis, Bronn., formerly arranged with Dapedius 

 and Amhlyurus (and which also included a large number of species 

 now classed under jEchmodus), has been shown by Sir P. Egerton to 

 be a "Pycnodont" closely related by its dentition to the genus 

 Microdon, and having the scales differently arranged and articulated ; 

 instead of the interlocking pegs and notches by which the scales of 

 Amblypterus and allied genera are joined, " each scale bears upon its 

 inner anterior margin a thick solid bony rib, extending upwards be- 

 yond the margin of the scale, and sliced off" obliquely above and 

 below, on opposite sides, for forming splices with the corresponding 

 processes of the adjoining scales."* 



The genus JEcJimodus was instituted in 1854* to include several 

 species formerly arranged under Tetragonolepis by Agassiz, but 

 which were found by Sir Philip Egerton to present certain distinct 

 characters. These are jEchmodus (Tetragonolepis, Ag.) angulifer, 

 confluens, dorsalis, heteroderma, LeacJiii, leiosomus, ovalis, pholidotus, 

 pustidatus, radiatus, speciosus, mastodonteus. Thus dismembered, 

 Tetragonolepis contains but one British species, T, discus. Eg., for 

 the T. mnnilifer and striolatiis are now referred to Dapedius and T. 

 mastodonteus, (Ag. 2, p. 216 to 23e., f. 3-5), is probably a Lepidotus. 



The main difference which exists between jEchmodus and Dapedius 

 consists in the character of the teeth, the former being unicuspid, 

 the latter bicuspid, as shewn in Figs. 2 and 3, Plate X. 



The specimen figm-ed (Plate X.) presents the following characters : 



Body short, orbicular, compressed ; length from the opercular plate 



1 Among the many examples of Fossil Fishes belonging to this genus which are 

 preserved in the National Museum, Mr. "W. Davies (to whom I am exceedingly in- 

 debted for much valuable assistance in drawing up this paper, and whose knowledge 

 of Fossil Ichthyology is very extensive) assures me that no trace of a decided bony 

 column exists in any well authenticated species of Lepidotus with the exception of 

 Lepidotus serrulatus from the Lias of Barrow, and L. Jimhriatus from Lyme Eegis, 

 both of which species, from other peculiarities, may eventually be found to form a 

 sub-genus. I am therefore led to conclude that the complete ossification of the noto- 

 chord is not a characteristic point in Lepidotus, as stated by M. Pictet. Prof. Pictet 

 says, op. cit. p. 161, Le Lepidotus Jimhriatus, Ag. est une espece dont la position 

 generique est encore douteuse. Les ecailles ont une fine dentelure sur leur bord. Le 

 L. serrulatus, Ag. a des rapports avec le L. gigas, mais en differe, ainsi que de pres- 

 que tous ses congeneres, par ses ecailles qui sont plus etroites vers le bord ventral. 



- Mem. Geol. Survey, 1861. Decade x. p. 28. 



3 Quart. Journ. Geol. Soc, Vol. ix. p. 276. 



1 Egerton, Quart. Journ. Geol. Soc, 1854, Vol. x. p. 367. 



