Notes on Ca^'honiferous' Soiachii. 419 



stone, Beith (Carboniferous Limestone series), which was 

 apparently undescribed. It is small, flattened, and broadly 

 triangular, the anterior margin being 1 inch in length, the 

 posterior If inches, the base | inch in breadth. The apex ends 

 in a sharp spike ; and just below this, on the posterior margin, 

 are two others, directed backwards. Externally the surface 

 is ornamented with distinct furrows, running parallel to the 

 anterior and posterior margins, consequently tending to radi- 

 ate from the apex towards the base, and giving the surface a 

 feebly ribbed appearance. On these ribs are small tubercles, 

 irregularly placed towards the apex, then becoming arranged 

 in lines which proceed obliquely, or with a slight sigmoid 

 curvature, across the surface from behind, downwards and 

 forwards. I have seen other specimens of the same spine 

 from the Carboniferous Limestone " bone-bed " at Abden, 

 Fifeshire, collected by Messrs W. Anderson and W. Tait 

 Kinnear, which show that the walls were thin, and the spine 

 consequently extremely hollow. In these specimens the ex- 

 ternal ribbing is also feebler, and the tubercles more thickly 

 placed. 



In their general configuration, and in the nature of their 

 surface ornament, the resemblance of this spine to Oracan- 

 thus is obvious, although the posterior area is not so sharply 

 defined, and though neither of the sides is notched or 

 sinuated on the lower margin as is, so far as my observation 

 goes, usually the case in the genus mentioned. It has, 

 perhaps, still thinner walls than the typical Oracanthi, and 

 might on that account be referred to St John and Worthen's 

 genus Pnigeacanthus ; but the generic distinction of this from 

 Oracanthus is doubtful. No Oracanthus has hitherto been 

 described with spikelets at the apex; but as the apices are 

 more or less worn, a ready explanation of their, absence is 

 obtained. I, therefore, designate this spine Oracanthus armi- 

 gerus, with the remark that if it be not a true Oracanthus, it 

 is an excessively closely allied form. 



Mr Davis recognises that the spines of Oracanthus existed 

 in pairs, and are not bilaterally symmetrical, having one side 

 larger than the other ; but when he refers them to the " pos- 

 terior termination of the body," hints at removing the genus 



