1866.] TOFNG PLA.TTSOMUS. 315 



Many specimens of this genus from the Fifeshire Carboniferous 

 rocks are in the Museum of St. Andrews, but the head in all these 

 specimens is imperfect. In the British Museum there is a specimen 

 which, in all save " the dimple," might be that from which Miller's 

 description was taken. The tritores and their sockets are well seen ; 

 not all are of equal breadth, some seeming of smaller diameter and 

 thinner root, a difference comparable to that seen among the teeth 

 of Pycnodonts. The teeth seem, as Miller has stated, undoubtedly 

 palatal, and, as such, disposed in several rows. The small opportu- 

 tunity I have had of studying Eurynotus, prevents me from doing 

 more than expressing my belief that the structure of the head agrees 

 with that of Mesolejns, the operculars being narrow and the supra- 

 scapulars elongate, as in that genus. The form and position of the 

 dorsal, ventral, and anal fins are also similar, while the nuchal line 

 to which Miller draws attention has the same characters in both 

 genera, and in others which are included under Lejpidopleuridce. 

 The external ornament of the scales differs wholly in kind ; but to 

 this less weight is due than to the absence of the back-stays, which 

 linger in reduced dimensions on the anterior scales of Mesolepis. 

 That name was selected to express the transitional character of the 

 genus, and Eurynotus supplies the next step in the departure from 

 the Lepidopleurid type. Wherever, therefore, Mesolepis is placed, 

 there Eurynotus must also go. The cranial structure, traced through 

 the other genera of the suborder, cannot be demonstrated in these 

 two forms, but complete specimens would probably not depart far 

 from it. The dental characters seem decisive, and warrant the 

 juxtaposition of Mesolepis and Eurynotus as aberrant forms of the 

 Lepidopleuridce. Amblypterus, the genus they approach nearest in 

 shape, is widely separated from them by its dentitional characters, 

 which, as well as its cranial anatomy, place it among the Lepidos- 

 teidce, not far from Oxygnathus. Nor is Lepidotus less distinct, as 

 appears from Quenstedt's valuable memoir. 



The five- genera just described form, with the family of Pycnodonts, 

 a natural group by which the Ganoid affinities of the latter are in- 

 creased, its Teleostean relations being at the same time brought into 

 greater prominence. The least variable common feature is the 

 structure of the scales, whence the name Lepidopleuridce may be 

 given to the group, whose definition is as follows : — 



Suborder Lepidopleijrid^*. 



Ganoids with heterocercal equilobate tails. Body rhomboidal, 



* The word " pleurolepida," appHed by Sir P. Egerton to the articular back- 

 rib of Pycnodont scales, has been altered to " lepidopleura," partly to render the 

 term more descriptive, partly to secure euphony in the subordinal title. The 

 solid advantage which excuses the change is, that confusion is thereby avoided 

 between Lepidopleuridce as above defined, and Fhurolepidce as used by Quenstedt 

 (Handb. der Petrefactenkunde, p. 209). The latter name includes the Pycno- 

 donts, and along with them Placodus, the group being stated to be intermediate 

 between Chondrostean and Holostean Ganoids, i. e. those on the one hand in 

 which scales and head-bones are the chief fossil remains, and those on the other 



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