218 



Mr. T. Stock on a Spine from the 



back- 

 greater 



the lower was free. A small piece 

 of about 7 millims. had been re- 

 moved by Mr. Taylor, with the in- 

 tention of preparing a microscopic 

 section from it. The length of the 

 spine as it exists is 18'4 centims. ; 

 in its perfect condition it was consi- 

 derably longer. The base is broken 

 short off at what must have been an 

 appreciable distance above the point 

 at which the spine entered the body 

 of the fish, as no trace of the inserted 

 portion remains. Its greatest dia- 

 meter, which is at the base, is 9 

 millims. It curves gently 

 wards ; the curvature is 

 towards the point than towards the 

 base. The apex itself is rather 

 finely pointed and enamelled with 

 ganoine. The ornament consists of 

 numerous fine, longitudinal, slightly 

 irregular stria? ; it covers the whole 

 of the existing surface with the ex- 

 ception of the tip. The grooves 

 are narrower than the ridges, and 

 smooth. Fracture shows that the 

 pulp-cavity occupies the greater 

 length of the spine. It is circular 

 in shape, and, as is usually the case, 

 is placed a little posterior to the 

 median line. Its walls are thick. 

 The anterior aspect is very convex 

 throughout. On the posterior aspect 

 is a prominent ridge, sloping to the 

 left lateral margin at an average 

 inclination of 35°. Between the 

 summit of the ridge and the right 

 lateral margin there is a groove, 

 extending from the tip to the base. 

 The middle third of the ridge is 

 very gently undulated. In the 

 groove are a few irregular pits ; 

 two of them may be seen about 

 halfway between the point and the 

 base, four near the apex. At first 

 I supposed that these pits were the 



Fiff. 1. 



1 



si mi 



iftff. a 



Fig. 1. Lophacanthus Tay- 

 lori, mihi ; f nat. size. In 

 the Collection of Mr. Joseph 

 Taylor. 



Fig. 2. Ditto ; f nat. size, 

 cross section. 



