FROM THE ISLE OF WIGHT. 281 



bordered on each side by a slightly elevated ridge, and sur- 

 rounded in front by a partially raised margin, which has 

 evidently given attachment to a powerful muscle for elevating 

 and fixing the spine. The symmetrical form and general out- 

 line of this process, will be better understood from the accom- 

 panying figures, than from any description however detailed. 

 Of the lateral processes, the right alone remains ; this is short- 

 er and less symmetrical than that just described, more gra- 

 dually rounded on the outer margin, coarse and open in its 

 texture, and irregularly convex on the under surface. Its 

 general direction forms an angle of about 45° with the cen- 

 tral process ; and the whole fossil bears a not unapt resem- 

 blance to the foot of a minute tapir or rhinoceros. What 

 may be called the heel, or junction of these three processes, 

 is likewise irregularly convex, and forms a continuous curve, 

 when viewed sideways, with the fragment of the spine itself. 

 This, of which unfortunately a small portion alone remains, 

 is of a very dense and compact structure internally, as may 

 be seen by the newly-fractured surface, beautifully striated 

 externally, and of large dimensions compared with the size 

 of the whole fragment. This basal portion exhibits none 

 of the enamel so apparent in the specimen described by Mr. 

 Charlesworth ; but it turns forward in the same direction, and 

 appears to have pretty nearly the same general curvature. 



However similar the specimen at present under considera- 

 tion may be to that described in the last number of the Ma- 

 gazine, in its general form and characters, it is nevertheless 

 very distinct in those minor traits which constitute specific 

 differences ; as might indeed be naturally expected from the 

 geological position of the deposits in which they were respec- 

 tively found. The bony base of the wealden species is not 

 more than half the size of that from the lias, though the spine 

 itself is equally large ; the former, as already mentioned, is 

 more symmetrical in form and closer in texture ; and the la- 

 teral processes, instead of standing out at right angles to the 

 central, have a more forward direction, whilst all the process- 

 es are longer and more slender. The following are some of 

 the principal comparative dimensions of both. 



LIAS WEALDEN 



SPECIMEN. DITTO. 



Half distance between the tips of the lateral processes ... .85 in. .45 in. 



Distance from the heel to the point of the middle process 1.2 .87 



Breadth of the central part of the middle process 55 .28 



marginal rim surrounding front of ditto .633 .34 



As respects the Hybodus Delabechei, the two latter mea- 

 surements must be received with caution, as the specimen has 

 been a little injured in this part by the process of clearing 



