282 SUPPOSED FRONTAL SPINE OF HYBODUS 



away the surrounding lias ; which may also account for its 

 less symmetrical form, unpolished surface, and the absence of 

 the marginal rim. The processes in both cases unquestiona- 

 bly gave attachment to powerful moving muscles ; the central 

 serving to direct the spine forwards, the lateral to either side, 

 and all to fix and steady it. From the more expanded direc- 

 tion of the lateral processes, also, the spine of Hybodus Dela- 

 bechei must have been capable of a greater extent of motion 

 from side to side than that of the wealden species ; and the 

 nature of the instrument itself shows that it must have been 

 a powerful weapon of offence. The specimen here described 

 farther proves that, like the horn of the rhinoceros, it was 

 connected with the bones of the skull, only by muscles ; but, 

 unlike, that instrument, it must have possessed great powers 

 of motion. M. Agassiz, is said to have a manuscript note of 

 the only species of Hybodus which has been hitherto disco- 

 vered in the wealden formation. Whether the fragment here 

 described may eventually prove to belong to that or a dif- 

 ferent species, time must determine ; but it is interesting to 

 know that the character of the frontal spine, first discovered 

 by Mr. Charlesworth, is not confined to the Hybodus Dela- 

 bechei, but common to the whole genus ; or at least to the 

 males, as in the allied genus Chimara. 



Art. V. — Letter addressed to the Editor by Henry Woods, Esq., 

 F.L.S., &c, respecting the supposed Frontal Spine of Hybodus in 

 the Bath Museum. 



30, Henrietta St., Bath, 



May \2th, 1839. 



My Dear Sir, 



A letter addressed by you to Mr. H. Jelly 

 (who, I am sorry to state, has been for some time absent from 

 Bath in consequence of ill health) having been handed over 

 to me, I proceed to give you as good an answer as is in my 

 power. 



Before the receipt of your letter to Mr. Jelly, I had search- 

 ed over the Museum of our Institution for the specimen men- 

 tioned by Mr. Lonsdale, and was fortunate enough to find it, 

 or at least that which I consider to be it ; and here you have 

 the best drawing I can make, which I hope is precise enough 

 for your purpose. It is of the natural size, and, from some 

 peculiarities, may indicate another species of Hybodus : fig. 

 38, a, is a lateral, and b a dorsal view of it. The specimen 

 measures lj inch in length, and -/-§• of an inch in breadth 



