18 riSH OF THE CARBONIFEROUS PERIOD. 



surface becomes polished and porous as in the P. porosus (Ag.), 

 and as we constantly see on the prominent parts of the P. ru- 

 gosus (Ag.). Length generally about 2 inches. 



Rare in the Armagh limestone. 



(CoL of the University of Cambridge and of Capt. Jones, M.P.) 



Helodus appendiculatus (M'Coy). 



Sp. Char. Transversely trigonal, compressed, width of the base 

 rather more than twice the greatest height of the tooth ; crown 

 divided into an obtusely trigonal, straight, central compressed 

 cone, and one very small, accessory similarly-shaped one on 

 each side, sharply defined by a distinct notch ; surface smooth, 

 highly polished, porous at the apex and posterior side of the 

 edge of the principal cone ; edge of the enamel-like surface at 

 the base obtuse, forming a slightly arched line, concavity 

 downwards : bony root large, simple, coarsely fibrous. 



Three teeth in situ, one behind the other, present the fol- 

 lowing characters : — the anterior tooth is the smallest, most 

 compressed, and perfectly erect; principal cone sharp, but its 

 height scarcely exceeding one-third of its width ; secondary cone 

 on each side very small, not as deeply separated from the middle 

 as in the others; entire surface highly polished with the ex- 

 ception of the apex, which is slightly punctured. The second 

 tooth is the longest and thickest, slightly inclined backwards; 

 height of the principal cone about half its width ; apex obtuse, 

 small accessory cone on each side, pointed and defined by a deep 

 notch from the central one; anterior side flattened, smooth, 

 polished ; posterior side tumid, coarsely punctured, the punctures 

 extending over the apex. Third tooth entirely procumbent, the 

 apex of the cone being marginal and in contact with the long, 

 coarsely fibrous, osseous base, which latter is truncate below, is 

 as wide as the tooth, and equals the principal cone in length : 

 the proportions of this tooth are nearly those of the middle one, 

 but having no posterior side ; anterior side smooth and polished, 

 apex punctured. 



Rare : from the carboniferous limestone of Armagh. 



(CoL Capt. Jones, R.N.) 



Helodus rudis (M^Coy) . 



Sp. Char. Irregularly oblong, subquadrate ; sides steep, irregu- 

 larly nodulose or undulato-plicate ; crown irregularly gibbous, 

 the highest point a little nearer one end than the other; sur- 

 face polished, coarsely punctured. Length 7 lines, width 4J 

 lines, height 2^ lines. 



The curiously irregular lump-like figure and quadrate base of 



