On some new Fossil Fish of the Carboniferous Period. 115 



XII. — On some neiv Fossil Fish of the Carboniferous Period. 

 By Frederick M'Coy, M.G.S. & N.H.S.D. &c. 



[Continued from p. 10.] 



Placoides. 



(Ichthyodorulites.) 



Homacanthus macrodus (M^Coy). 



Sp. Char. Spine about 8 lines long and 2 lines wide at base, 

 slightly arched and tapering to a point ; section compressed, 

 trigonal ; anterior face formed by a narrow rounded keel, pos- 

 terior concave face bounded on each side by a larger rounded 

 ridge, between which and the anterior keel there is on each side 

 a still smaller rounded longitudinal ridge, the two posterior 

 ridges on each side dichotomise near their base ; of the two 

 intervening spaces the anterior is rather wider and the poste- 

 rior rather narrower than the ridges which they separate, they 

 are concave and very slightly striated longitudinally ; posterior 

 face with twelve or fourteen very large, compressed, falcate 

 teeth, alternating in two rows, the alternating bases touching, 

 keeled on their convex edge, their length nearly equalling the 

 width of the side of the ray at their base. 



The small size, few ridges and great posterior teeth easily di- 

 stinguish this from other rays of the carboniferous period, while 

 the two latter characters equally distinguish it from the H. ar- 

 cuatus (Ag.) of the old red sandstone. This genus has not been 

 noted before in the carboniferous series. 



Rare in the carboniferous limestone of Armagh. 



[Col. University of Cambridge.) 



Homacanthus microdus (M^Coy). 



Sp. Char. Spine about 1^ inch long and 2 lines wide at base ; 

 very slightly arched, gradually tapering ; section ovate ; ante- 

 rior face formed of a narrow rounded keel, each side with two 

 slightly flattened nearly equal keels, the posterior one dicho- 

 tomous at its base ; they are their own width apart, the inter- 

 vening spaces being flat and marked with about three longi- 

 tudinal strise ; posterior face with two rows of numerous, co- 

 nical hooked teeth, their length scarcely one-fifth the width of 

 the ray at their base. 



The more slender form, flattened ribs and interspaces, and 

 numerous small conical teeth distinguish this from the last, with 

 which alone it is likely to be confounded. 



From the same locality and in the same collection as the last. 



8^< 



