FROM LYME REGIS. 245 



A very strong and irregularly shaped bone arises from the 

 centre of the mass, and, with its base apparently resting up- 

 on this bone, is placed the curved spine which constitutes 

 the principal feature of interest in the present specimen. — 

 From the position which this spine now occupies, it would 

 appear to have been situated about the region of the head, 

 bending abruptly forwards directly it emerged from the in- 

 teguments. The apex of the spine is unfortunately broken 

 off; but the portion left is about half an inch long, covered 

 with a smooth glistening coat of enamel, and presenting a 

 slight but well-defined upper edge. A few elevated and wa- 

 vy striae are irregularly distributed upon its surface. The 

 spine arises from a strong, expanded, bony base, which is 

 formed by three obtuse processes united in a common centre, 

 one of them extending anteriorly in the median line, and the 

 other two, which may be termed the lateral processes, at right 

 angles to the anterior one. Some portions of the surfaces of 

 these processes would appear to have given attachment to 

 very strong muscles, (fig. 7 & 8). 



At the first glance this hooked spine might be thought to 

 be related to those which characterise so many species of the 

 genus Raia of Linnaeus, but its remarkable bony base, and 

 the general aspect of the organ itself, would seem to indicate 

 its connexion with more important functions than are pos- 

 sessed by a mere dermal prickle. In the absence of evidence 

 to the contrary, I should feel disposed to regard it as a soli- 

 tary spine, developed in the median line of the frontal region, 

 and connected with or simply resting upon the bones of the 

 cranium. In the Chimera monstrosa, to which Hybodus has 

 some affinity, a horn or frontal process is also present. In this 

 instance, however, it is only found in the male sex, and the 

 process itself has none of the formidable character about it 

 presented by the spine of Hybodus ; having but a compara- 

 tively slight base, and though the apex is armed with a series 

 of small prickles, the process itself is, I believe, externally 

 fleshy, with an internal, slight, bony support. The apparent 

 analogy, however, is worth a passing notice, because the teeth 

 of Chimera, although an existing genus, have been found fos- 

 sil in deposits which also contain the remains of Hybodus. 



The teeth in the present specimen vary from half an inch 

 to three quarters of an inch in length. They are slightly 

 bowed, with the convexity outwards, and at the same time 

 arched from above to below, so that the apices of the outer- 

 most lateral lobes, in many instances, are nearly on the same 

 level with the base of the central process. The crown of the 

 tooth slightly projects beyond the osseous root which con- 



