628 BRITISH PALAZOZOIC FOSSILS. [ Pisces. 
Genus. ERISMACANTHUS (M/‘Coy). 
(Ltyim. épecpa, a prop or stay, and aavOa, a spine.) 
Dese.—Spine of three divaricating portions ; first, a large compressed, finely striated base, which entered 
the flesh; secondly, a short, strongly compressed, rapidly tapering spine, curved directly backwards, the sides 
marked with strong, smooth, longitudinal ridges, and having two rows of short, downward curved teeth on the 
posterior concave margin ; thirdly, a peculiar prop-like portion extending directly forwards nearly at right angles 
with the base, gently arched downwards, compressed at the basal half, depressed at the distal half, closely 
covered with blunt, smooth, oval tubercles, and with some large, irregular spines on the under side; the portion 
of the base above the flesh, and from which these two portions branch, is irregularly tuberculated. 
The long anterior prop or stay-like branch renders this ichthyodorulite so unlike any described form, that 
I should have hesitated to describe it, but for the number of examples which I have recently examined. Some- 
thing slightly analogous I observe in the articulation of the spines of the recent fish allied to Synodontus, in which 
a shorter but similarly curved and directed prop-like process may be observed, but which is concealed beneath the 
soft parts, and not external, as in the fossil. I know but one species of the genus, which I have great pleasure in 
dedicating to Capt. Jones, R. N., M. P. &c., who is in possession of more extensive and exact knowledge of the 
fossil fishes of the mountain-limestone, than I believe any other observer. It is to his acumen in recognising the 
true characters of the species, zeal in collecting, and liberality with which both his cabinet and information are 
made available to those studying the subject, that we are mainly indebted for the extended lists which have been 
published of the Jchthyolites of this formation. 
ErisMAcANTHUS Jonesir (A/’Coy). Pl. 3. K. fig. 26, 2 
hef.—MCoy, Ann. Nat. Hist. 2nd Series, Vol. IT. p. 119. 
Desc.—Posterior spine little more than twice as long as wide, slightly curved, compressed, sides flattened, 
with about eight or nine longitudinal ridges, which are smooth and less than their own diameter apart; the 
intervening spaces finely striated longitudinally ; posterior concave face with two regular, close rows of small 
pointed teeth directed very obliquely downwards, the surface towards the base is marked with small, scattered, 
oval, smooth tubercles; anterior branch three times as long, and about the same size at its origin as the 
posterior spine; the part of the spine from which those two portions take their common origin is equal to 
the width of their united bases, and covered with scattered round tubercles; the height of the anterior branch 
is double its width at the basal half, but it becomes depressed, so that its width is aoe the height in the 
section of the distal half; it is covered above and on the sides with close, quincuncially arranged, emotes oval 
tubercles; the compressed, finely striated base which enters the flesh seems abruptly tr eed below. Length 
of posterior spine one inch, width at base six lines; length of anterior process (imperfect at extremity) two arahes 
nine lines, depth at base four lines, at tip one line; width at base two lines, at tip three lines; length of the 
common base one and half inch, width nine lines. 
Position and Locality.— Not very uncommon in the carboniferous limestone of Armagh. 
Explanation of Figures.—P|. 3. K, fig. 26, dorsal spine shewing the posterior spine, imperfect at the apex, 
and the anterior prop-like branch, denuded of some of its tubercles, the base of insertion also absent ; fig, 27, 
ditto dotted outline shewing the perfect form (from the collection of Capt. Jones, R. N., M. P.) shewing the 
base of insertion, anterior ead posterior branches, and denticulation of the latter; fig. 27a, ditto compressed 
section of base of anterior branch ; fig. 27 6, ditto portion of anterior branch with the duboreulation perfect ; fig. 
27 c, ditto depressed section of extremity of anterior branch ; fig. 27 d, section of posterior spine, natural size. 
