146 
1CHTHY0D0BT7LITES. 
ornament or layer of ganoine ; an unsymmetrical double longi¬ 
tudinal series of denticles on the posterior aspect distally. 
This genus is not represented in the Collection, and is known 
only by the type species :— 
Aganacanthus striatulus , It. H. Traquair, loc. cit. p. 64.—Middle 
Carboniferous Limestone (Blackband Ironstone) ; Borough 
Lee, near Edinburgh. [Collection of Dr. It. H. Traquair.] 
Probably to this group of Ichthyodorulites may also be assigned 
the following genus and species :— 
GompJiacanthus acutus, J. W. Davis, Quart. Journ. Geol. Soc. 
vol. xl. (1884), p. 618, pi. xxvi. fig. 9.—Lower Carboni-’ 
ferous (Yoredale Bocks) ; Wensleydale, Yorkshire. [York 
Museum.] 
IV. Spines probably not placed in advance of fins, but most nearly 
resembling the head-spines of the male Chimaeroids and some 
Mesozoic Cestraciont Sharks (e. g. Hyhodus). 
Genus ERISMACANTHUS, M‘Coy. 
[Ann. Mag. Nat. Hist. [2] vol. ii. 1848, p. 118.] 
Syn. Cladcicanthus, J. W. Davis (ex Agassiz, MS.), Trans. Boy. Dublin 
Soc. [2] vol. i. 1883, p. 364. 
Basal portion of spine broad, laterally compressed, not deeply 
inserted, soon bifurcating above into two slender divergent branches 
in the same vertical plane ; one branch considerably arched, keeled, 
and pointed distally, with a series of denticles upon the concave 
margin ; the other branch longer, not tapering to a point, but ter¬ 
minating in a cluster of elongated tubercles. An internal cavity 
extending throughout the spine. Superficial ornament of exserted 
portion consisting of tubercles and sulcations, the latter predomi¬ 
nating in the short pointed branch of the spine. 
Erismacanthus jonesi, M‘Coy. 
1843. Clcidacanthus paradoxus , L. Agassiz, Poiss. Foss. vol. iii. p. 176 
(name only). 
1848. Erismacanthus jonesii, F. M‘Coy, Ann. Mag. Nat. Hist. [2] 
vol. ii. p. 119. 
1848. Dipriacanthus falcatus , F. M'Coy, ibid. p. 121. [Mus. Geol. 
Soc. London, j 
