CESTRACIONTIDJE. 
241 
Genus DICLITODUS, Davis. 
[Trans. Key. Dublin Soc. [2] vol. i. 1883, p. 410.] 
An indefinable Carboniferous genus, known only by the teeth, 
which are of very small size, narrow and elongated. The dental 
crown is elevated at each extremity and depressed mesially. 
Diclitodus scitulus, Davis. 
188.3. Biclitndus scitulus, 3. W. Davis, Trans. Roy. Dublin Soc. [21 
vol. i. p. 410, pi. li. fig. 29. 
1884. BicUiodus scitulus, 3. W. Davis, Quart. Journ. Geol. Soc. vol. xl. 
p. 023, pi. xxvii. tig. 12. 
Ty/jc. Detached tooth ; Horne Collection, York Museum. 
The single known species. 
, Form. 4" Loc. Upper Carboniferous Limestone : Yorkshire. 
49629. Tooth ; Richmond. Purchased, 1878. 
P. 4890. More imperfect tooth ; Yoredale Rocks, Wensleydale. 
Home Coll. 
P. 4891. Tooth on slab, with PUuro^lax and Pctalodus ; Wensley- 
Home Coll. 
Genus SPHENACAJMTHUS, Agassiz. 
[Poiss. Foss. vol. iii. 1837, p. 23.] 
Teeth moderately high, with a large principal coronal cusp, and 
smaller lateral cusps diminishing in size outwards, more or less 
marked by superficial wrinkles; root depressed, forming a slight 
expansion backwards. Dorsal fin-spines ornamented by robust 
longitudinal ridges, in part nodose; posterior denticles small, 
numerous, in two scries, one upon each lateral margin of the 
flattened or slightly concave posterior face. Cephalic spines appa- 
rently absent’ ; shagreen sparse, consisting of minute comb-shaped 
granules. 
Though the dorsa fin-spines of this fish arc indistinguishable from 
those named CUnacanthus by Agassiz, the absence in the Carboni- 
ferous Limestone of teeth gcncrically identical with those just de- 
scribed indicates that the ichthyodorulites in question are common 
to more than one genus. The writer thus ventures to foDow a 
’ The spine assigned to the head by J. Thomson (Trans. GeoL Soc Glasgow 
vol. iv. pt. i. 1871, p. 59, pi. iii. fig. 2) is evidently a dorsal spine of Plcuracaufkus. 
K 
