250 Messrs. Hancock and Atthey on a nearly entire 



posterior tapering extremity of the body, which has lost the 

 tail, and is a little less than two inches wide across the tho- 

 racic expansions, which are just behind the head. The con- 

 tour is much obscured by the scattering of the tubercles com- 

 posing the shagreen ; and the slab has been broken away so 

 as to remove a part of the left side of the specimen. A por- 

 tion of the counter slab, however, has been saved ; and on this 

 the left thoracic expansion is sufficiently revealed. The head 

 (Pl.XVII.fig,l,ffl) lies immediately in front of and in connexion 

 with the body, but it is so much distorted that the form 

 cannot be determined : it is about five eighths of an inch long. 

 No bones are distinguishable ; but the substance is here a little 

 thickened, indicative of the cartilaginous remains of the cra- 

 nium ; nor is there anywhere in the body the least appearance 

 of bones, the skeleton undoubtedly having been cartilaginous 

 throughout. The teeth {b) lie within the area of the head, in 

 a disturbed condition, some with the crown uppermost, others 

 with it downwards. They do not seem to have been numerous, 

 but are so obscured that the exact number cannot be ascertained. 

 In the detached head, however, ten or a dozen can be counted j 

 but there is no certainty that the number may not have been 

 greater ; indeed it is probable that some have been removed 

 with the counter slab. 



The body suddenly widens immediately behind the head, 

 the width being considerably increased by the thoracic expan- 

 sions (c, c) , which extend about half \vay down and appear to 

 have had their margins pointed ; thence it tapers backwards, 

 and soon dies out, there being no definite indication of the 

 form of this portion ; and, as has been already stated, there 

 is no trace of the tail. The spine {(T) is situated a little 

 behind the thoracic expansions ; consequently it is nearer the 

 posterior than the anterior extremity. It projects from the 

 dorsal margin, and is inclined backwards, apparently in its 

 natural position, marking the situation of the dorsal fin-; but 

 no traces of this remain. About two thirds of the spine is in a 

 good state of preservation, the other third being well and 

 sharply defined in cast ; it is straight and stout in proportion 

 to its length, and tapers somewhat abruptly to a sharp point ; 

 it is compressed laterally, with tlie anterior margin thicker 

 than the posterior ; the surface is coarsely and irregularly 

 grooved and ridged longitudinally ; it measures five eighths 

 of an inch in length, and is at the thickest part one eighth of 

 an inch wide. 



Shagreen covers the whole of the specimen, defining its 

 extent and form, though, as already noticed, with no great 

 precision, as the margins are much blurred by the displace- 



