CESTEACIOXTIDiE, 
241 
Genus DICLITODUS, Davis. = ‘ ^ 
[Trans. Roy. Dublin Soc. [2] vol. i. 1883, p. 410.1 
, i 3 0 & *- 
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. 
1883. Diclitodus scitulus, J. W. Davis, Trans. Hoy. Dublin Soc. [2] 
vol. i. p. 410, pi. li. fig. 29. 
1884. Diclitodus scitulus, J. W. Davis, Quart. Journ. Geol. Soc. vol. xl. 
p. 623, pi. xxvii. fig. 12. 
Type. Detached tooth ; Horne Collection, York Museum. 
The single known species. 
Form. Sf Log. Upper Carboniferous Limestone: Yorkshire. 
49629. Tooth; Richmond. Purchased, 1878. 
P. 4890. More imperfect tooth ; Yoredale Hocks, Wensleydale. 
Horne Coll. 
P. 4891. Tooth on slab, with Pleuroplaoc and Petalodus; Wensley¬ 
dale. Horne Coll. 
Genus SPHENACANTHUS, Agassiz. 
[Poiss. Loss. 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 series, one upon each lateral margin of the 
flattened or slightly concave posterior face. Cephalic spines appa¬ 
rently absent 1 ; shagreen sparse, consisting of minute comb-shaped 
granules. 
Though the dorsa fin-spines of this fish are indistinguishable from 
those named Ctenacanthus by Agassiz, the absence in the Carboni¬ 
ferous Limestone of teeth generically identical with those just de¬ 
scribed indicates that the ichthyodorulites in question are common 
to more than one genus. The writer thus ventures to follow a 
1 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 Fleur acanthus. 
E 
