48 



PISCES 



CLASS I 



Edaphodon, Buckland (Passalodon, Buckl. ; Eumylodus^ Mylognathus, Leidy ; 

 Dipristis, Marsh; Leptomylus, Cope), (Fig. 93). Lower dental plates with a 

 broad symphysial facette ; posterior upper dental plates tapering in front, 

 truncated behind, and with three tritors. Cretaceous, Eocene, and Oiigocene 

 of Europe and North America. 



Elasmodedes, Newton (Elasmognathus, Newton, non Gill). Mandibular teeth 

 laterally compressed and trenchant, with a series of small tritors along the 

 oral border. E. willetti, Newton, from Lower Chalk, Kent. 



Amylodon, Storms. Lower Miocene (Rupelian) ; Belgium. 



Elasmodiis, Egerton. Upper Cretaceous of Belgium ; Eocene of England 

 and Prussia. 



Dental plates of the existing genus Callorhynchus, Gronow, have been 

 identified from the Cretaceous of Amuri Bluff, New Zealand ; of the existing 

 genus Chimaem, Linn., from the Upper Tertiary of Europe and Java. 



roCi-Cv 



Ichthyodorulites. 



Fossil fin spines consisting of dentine or vasodentine, and thus presumably 

 referable to the Selachii, are frequently found isolated 

 especially in the Palaeozoic formations, and can only be 

 in part assigned to definite genera. These are therefore 

 described under provisional generic names. Most of them 

 are bilaterally symmetrical, and may 

 be regarded as median dorsal spines ; 

 but several are distinctly rights and 

 lefts, and belong either to the paired 

 fins, as in Acanthodidae, or to the side 

 of the head, as in Menaspis among 

 Cochliodontidae. In the unsym- 

 metrical spines, the base is, as a rule, 

 abruptly truncated ; in the bilaterally- 

 symmetrical dorsal spines, on the other 

 band, it is usually elongated and tapers 

 to the proximal end. 



Among the Ichthyodorulites not 

 yet referable with certainty to definite 

 genera or families, the following may 

 be enumerated . — 



(a) Slender, bilaterally-symmetrical 

 spines, with a smooth base sharply 

 separated from the exserted portion ; internal cavity open 

 posteriorly towards the base. Probably for the most part 

 referable to the Cestraciontidae. Onchus, Ag. (Fig. 94); 

 Upper Silurian and Devonian, Europe and eastern North 

 America. Ctenacanthus, Ag. (Fig. 95), possibly the fin 

 spines of Orodus ; Lower Carbonif erous, Europe and North 

 America. Homacanthus, Ag. ; Devonian and Lower Carboni- 

 ferous. AcondylacantJms, St. J. and Worth. ; Asteroptychius, 

 M'Coy ; Lispacanthus, Davis ; Geisacanthus, St. J. and Worth.; 

 Lower Carboniferous. Lepracanthus, Owen ; British Coal Measures. IFodniJca 



Fig. 94. 



Onchus tenuistriatus, Ag. 

 Fin-spine, iiat. size. Upper 

 Silurian ; Ludlow, England. 



Fig. 95. 



Ctenacanthus denticu- 

 latus, M'Coy. i/2!nat. 

 size. Carboniferous 

 Liniestone ; Monaduff, 

 Ireland (after M'Coy). 



