﻿IC IITI1 YODORULIXES . 



107 



Closely related to Homacanihus is the spine described as follows : — 



Hoplonchus, J. W. Davis (Quart. Journ. Geol. Soc. vol. xxxii. 

 (1876), p. 336), with the type species, E. 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. ■parvulus, J. S. Newberry, Palaeoz. 

 Fishes N. America (Mon. U.S. Geol. Surv. no. xvi. 1889), p. 169, 

 pi. xxv. fig. 5. This spine was previously described as Ctenacanthus 

 parvulus (J. S. Newberry, Eep. 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. 



Genus ACONDYLACANTHUS, 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 " genus," St. John & Worthen 

 include in it Ctenacanthus-shsi^ed 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. 



Acondylacanthus attenuatus, Davis. 



1883. Acondylacanthus attenuatus, J. W. Davis, Trans. Roy. Dublin 

 Soc. [2] vol. i. p. 352, pi. xlvi. fig. 3. 



Type. Woodwardian Museum, Cambridge. 



Form. Sf Loc. Lower Carboniferous Limestone : Armagh, Ireland. 



P. 2672, P. 2674-5. Three imperfect distal portions of spines. 



Ennislcillen Coll. 



