ICHTHY0D0RUL1TES. 
107 
Closely related to Homacanihus is the spine described as follows :— 
Hoplonclius , J. W. Davis (Quart. Journ. Geol. Soc. vol. xxxii. 
(1876), p. 336), with the type species, H. elegans , J. W. Davis, 
ibid. vol. xxxv. (1879), p. 183, pi. x. figs. 12-14.—Lower Coal- 
Measures ; Yorkshire. [J. W. Davis Collection, Halifax.] 
A second species is named H. parvidus, J. S. Newberry, Pakeoz. 
Fishes N. America (Mon. TJ.S. Geol. Surv. no. xvi. 1889), p. 169, 
pi. xxv. fig. 5. This spine was previously described as Ctenacanthus 
parvulus (J. S. Newberry, Hep. U.S. Geol. Surv. Ohio, vol, ii. pt. ii. 
1875, p. 55, pi. lix. fig. 3), and was obtained from the Cleveland 
Shale (Lower Carboniferous) of Ohio. J* 
St if 
Genus ACONDYLACANTHUSj St. John & Worthen. 
[Pal. Illinois, vol. vi. 1875, p. 432.] 
Dorsal fin-spines slender, elongated, laterally compressed and 
gradually tapering; sides of exserted portion ornamented with lon¬ 
gitudinal ridges, usually smooth, rarely crenulated or denticulated; 
posterior face concave, with a series of small denticles upon each 
margin, and sometimes with a median keel. 
As proved by specimens in the Collection (e. g. no. P. 2536 a) 
these slender spines have a short base of insertion, resembling that 
of Ctenacanthus. 
In their latest interpretation of this 4 ‘ genus,” St. John & Worthen 
include in it Ctenacanthus-shaapedL spines with smooth ridges, while 
long slender spines with denticulated ridges are placed in Ctena- 
canthus proper. We prefer, however, to follow Davis in regarding 
the form of the spine as the character of foremost importance. 
Ac on dyl acanthus attenuates, Davis. 
1883. Acondylcicanthus attenuatus, J. W. Davis, Trans. Roy. Dublin 
Soc. [2] vol. i. p. 352, pi. xlvi. fig. 3. 
Type. Woodwardian Museum, Cambridge. 
Form, df Loc. Lower Carboniferous Limestone : Armagh, Ireland. 
P. 2672, P. 2674-5. Three imperfect distal portions of spines. 
\ ,-r Enniskillen Coll. 
. , 4 ? , 
