CAlfNEL COAL OF THE WEST RIDIXG OF YORKSHIRE. 65 



the base the diameter diminishes rapidly, and at half an inch 

 from the apex it is -15 inch. This diameter is maintained for '4 

 inch, the spine then terminating abruptly in an obtuse point. 

 The spine may originally have been round ; it is now somewhat 

 compressed in form. The upper part is smooth, and covered with 

 hard black ganoine. The lower part is fluted with longitudinal 

 grooves, which increase rapidly in number by bifurcation. The 

 spine appears to be solid ; no internal cavity or canal can be distin- 

 guished in this specimen. Its base is composed of chondriform bone, 

 {. e. cartilage vrith numerous minute osseous centres, a very similar 

 structure to that of the semiosseous skeleton of Pleur acanthus. 

 Extending laterally from the base there is a mass of similar chondri- 

 form bone ; contiguous to the spine it is produced into two or three 

 short denticles. It then becomes thinner, but again develops into 

 a mass which may very well have served as the base of a second 

 spine, providing one was present (see fig. 3). There is no distinct 

 evidence, however, of a second spine having been present on this 

 specimen; it has rather the appearance of a thick scale, somewhat 

 acuminate towards the centre. 



The only fish-remains hitherto described which have any resem- 

 blance to these are comprised in the genus Byssacanthus* of 

 Agassiz. It is defined as containing spines more or less arched, 

 longitudinally furrowed, with the base much expanded. The spines 

 are about an inch in length and three quarters of an inch wide at 

 the base ; they converge rapidly to an obtuse point, and are more 

 or less arched ; deep grooves extend longitudinally along each lateral 

 expansion reaching quite to the point. In some respects Byssa- 

 canthus presents features similar to those of the spine described 

 above. Both are obtusely pointed and expanded towards the base ; 

 but whilst in Byssacanthus the anterior portion of the spine is round 

 and strong, the posterior is much expanded and appears to be very 

 thin. The basal portion in my specimen radiates equally in all di- 

 rections from the point ; the furrows in the latter indicate the homo- 

 geneous character of the spine by their similarity in form and 

 arrangement on all sides : in Byssacanthus they are very diff'erent ; 

 on the thick anterior portion the striations are parallel to the an- 

 terior margin and about equidistant, but on the posterior wing-like 

 expansion they diverge rapidly towards the base and become wide 

 apart. 



The spine in its character and its attachment to the dermal 

 covering of the fish bears a strong resemblance to the spines of the 

 existing Trunk-fish, Ostracion cornutus. The Trunk-fish is a small 

 squarely-built fish, protected by a covering of six-sided plates. On 

 its anterior and posterior extremities the dermal covering is pro- 

 duced so as to form four bony spines, broad at the point of insertion, 

 rapidly contracting, thence continuing about the same diameter for 

 a short distance, and ending in a point. The spines of the Trunk- 

 fish are long and slender in proportion to their breadth, being fully 

 three times as long as the diameter of the base. The fossil spine 



* Pois. foss. du Vieux Grea Eouge, tab. 33. figs. 11-14 and 15. 

 Q. J. G. S. m. 141. F 



