Z FISH OF THE CARBONIFEROUS PERIOD. 



trouble to make microscopic sections for me of the new genera ; 

 without their most valuable aid I could not have presented the 

 internal microscopic structure of those forms. 



CCELACANTHI. 



Holoptychius (Ag.). 



When we look to the large number of species of this genus now 

 known in the old red sandstone, all characterized by thick, bony 

 longitudinally plaited scales, and the largest of them having but 

 small conical teeth, sulcated at the base, and then compare them 

 with those large compressed teeth in the carboniferous shales, such 

 as the H. Hibberti (Ag.), of which Prof. Owen formed his genus 

 RhizoduSj and the nearly allied, if not identical, H. Portlocki (Ag.) 

 of the Irish shales, with their associated large, thin, rotundo- 

 quadrate scales having the minute reticulated structure of G/y- 

 ptolepis, I think it would be desirable, instead of considering the 

 genera Holoptychius and Rhizodus synonymous as they are now 

 held, to retain both generic names, but restricting each to such 

 forms as those above noticed. In this point of view the follow- 

 ing is the only true Holoptychius I have yet seen from the car- 

 boniferous limestone. 



Holoptychius Hopkinsii (M'Coy). 



Sp. Char. Scales elongate, narrow, elliptically pointed, very thick, 

 convex ; exposed portion strongly enamelled, covered with nu- 

 merous thick, rounded, slightly flexuous, anastomosing, longi- 

 tudinal ridges; concealed smooth portion deeply bifurcate, 

 generally bent laterally at a considerable angle with the ex- 

 posed portion. Length of enamelled portion 6 lines, width 3 

 lines. 



The thick, narrow form and strong longitudinal ridges of the 

 surface distinguish this species easily from its congeners. It 

 abounds in some parts of the black impure beds intercalated 

 between the carboniferous limestone and overlying shale of Der- 

 byshire, from whence the specimens described were collected by 

 W. Hopkins, Esq., who presented them, with a suite of fossils 

 from that district, to the University collection at Cambridge. I 

 have great pleasure in dedicating it to one who, as a mathema- 

 tician, and as an observer in the field, has so materially advanced 

 the science of geology. 



Isodus leptognathus (M'Coy). 



I provisionally apply the above name to a dentary bone of a 

 Ganoid fish apparently allied to Glyptolepis. It is destitute of 



