CESTRACIOJTTID^. 243 ; 
1876. Ctenacantlms hyhodoides, J. Ward, [Proc.] N. Staffs. Nat. Field- 
Club, p. 215. 
(?) 1878. Hybodm davisi, W. J. Barkas, Monthly Rev. Dental Surgery . 
vol. vii. p. 192. 
1878. Ilybodus, W. .1. Barkas, Proc. Roy. Soc. N. S. Wales, vol. xi. 
p. 145. 
Type, Dorsal fin-spine. 
A species larger than either of the preceding, and not yet pre- 
cisely defined. Crown of tooth robust and prominently striated; 
lateral denticles well developed. Ribs of the dorsal fin-spines 
generally smooth and rounded, sometimes in part nodose. 
The dorsal fin-spines named by Egerton Ctenacantlms hyhodoides 
and C. nodosus appear to the present writer to belong respectively 
to the anterior and posterior dorsal fins of the same fish. The 
nodose character of the superficial ornamental ridges varies greatly ; 
in all the specimens examined from Staffordshire and Derbyshire 
the ridges are smooth. 
Form. ^ Loe. Coal-Measures ; Scotch Coal-field, Northumberland, 
Yorkshire, Derbyshire, Staffordshire, and N. Wales. 
21428,21975. Three teeth, one having a smooth principal cone; 
Carluke, Lanarkshire. Purchased, 1847. 
P. 1322. Two teeth ; Longton, Staffordshire. Egerton Coll. 
P. 5234. Imperfect tooth ; near Dudley, S. Staffordshire. 
Purchased, 1880. 
36173. Supposed anterior dorsal fin-spine, with most of the orna- 
mental ridges slightly nodose ; Dalkeith, near Edinburgh* 
The posterior face is well shown, and also the extent of 
the posterior excavation. Purchased, 1862. 
P. 2222. Three spines of similar proportions, with the ornamental 
ridges less nodose ; Caudenfoot, Dalkeith. Egerton Coll, 
P. 3123. Two imperfect associated spines, perhaps pertaining to the 
two dorsal fins of one fish; Dalkeith. The exserted 
portion of one specimen would probably measure 0'265 
in length when complete, that of the other perhaps 
0-305. Both are similarly ornamented, most of the super- 
ficial ridges being finely nodose; but the fossil is too 
imperfect to allow of the precise relative proportions of 
the spines being compared. Ennislcillen Coll. 
P.3121. Type specimen of Ctenacanthus nodosus, Egerton; Dal- 
Ennislcillen Coll. 
B 2 
