428 J. W. DAYIS ON ANODONTACANTHUS, A NEW GENUS 



1. Anodontacanthus acutus, Davis. (Plate XXII. fig. 10.) 

 Spine. Length 2*5 inches, breadth *2 inch. The spine is straight, 



and gradually tapers to a point ; there are no denticles ; and 

 the surface of the spine is uniformly covered with little pittings, 

 giving an appearance of reticulation. The walls are about one 

 fourth the diameter of the spine in thickness ; there is an in- 

 ternal cavity with a wide open termination at the basal extremity, 

 the walls as they approach the base becoming much thinner. The 

 cavity extends along the interior of the spine almost to its apex. 

 The spine has every appearance of having originally been circular in 

 form. It has, however, become somewhat crushed along the basal or 

 weaker portion of the spine since its deposition. The specific desig- 

 nation acutus expresses its pointed character. 

 Locality. Cannel Coal, Tingley, Yorkshire. 



2. Anodontacanthus obtusus, Davis. (Plate XXII. fig. 11.) 



A spine from the same locality and horizon as the one already 

 described is of larger dimensions and different form ; the basal end 

 is broken off ; the remaining portion is 2*5 inches in length, and the 

 diameter nearly 0-3 inch. Judging from the proportions of the 

 spine preserved, it is probable that, including the missing portion, 

 its length would be 3*50 inches when perfect. The surface is uni- 

 formly covered with minute longitudinal striations, which towards 

 the apex become broken up into small pore-like indentations, the 

 latter being finer than in the smaller species. The portion of the 

 spine preserved maintains a uniform thickness to within an inch 

 of the apex, where it becomes slightly contracted, and ends in a 

 broad, flattened, obtusely rounded extremity, 0*2 inch across. The 

 body of the spine is oval in section, with an internal canal occu- 

 pying one third of its diameter. The spine differs from the one de- 

 scribed before in its greater size, oval form in section, extremely 

 broad apical termination, striated surface, and in the greater 

 thickness and strength of its walls. All together these differences 

 appear sufficiently great to render necessary a separate specific de- 

 signation ; and I propose to give it the name of A. ohiusus, in refer- 

 ence to its obtusely-pointed extremity. 



Locality. Cannel Coal, Tingley, Yorkshire. 



3. Anodontacanthus eastioiatus, Davis. (Plate XXII. fig. 12.) 

 Spine imperfect, the base absent ; part preserved 2*4 inches in 



length, extending from the point, apparently half the length of the 

 spine, the lateral diameter greatest, being 0*4 inch. It is oval in 

 section, least diameter between the anterior and posterior faces being 

 0*2 inch ; there is a central cavity, circular in section, which 

 extends towards the point. Prom the largest diameter of the spine, 

 it becomes gradually smaller, and ends in a somewhat worn-looking 

 point. The whole of the surface is covered with longitudinal stria?, 

 most distinct near the basal extremity, anastomosing and becoming 

 gradually less numerous towards the point, where the striae have 

 disappeared and the spine is smooth. 



