246 FOSSIL REMAINS OF HYBODUS 



nects it with the jaw, the line of separation being marked by 

 a well-defined sulcus. The crown is composed of a central 

 conical, blunt process, bounded on either side by four or five 

 small lobes, which are more or less distinctly developed. A 

 raised median line extends from the apex to the base of the 

 central process, both on the inner and external aspects, giv- 

 ing off* other lines, which diverge, ■ and spreading over the rest 

 of the process, become suddenly thickened just before they 

 reach its base. Upon the smaller processes or lobes of the 

 teeth, the lines also exhibit a strong tendency to converge to- 

 wards the large central one. The space between these raised 

 lines is about double that occupied by the lines themselves. 

 On the internal aspect of the teeth, the lines exhibit, in a 

 greatly diminished degree, the tendency to converge towards 

 the central process, (see fig. 4). In many of them indeed, over 

 the internal surface, the lines are vertical in their direction. 

 Below, and extending parallel to the groove which separates 

 the crown from the osseous root, is a prominent ridge, (see fig. 

 3), but of this there is no corresponding indication on the in- 

 ternal aspect, (fig. 4). 



The above description must be considered as applying to 

 the apparently normal or typical character of the teeth, many 

 modifications of which may arise from their position in a par- 

 ticular part of the jaw, or from accidental circumstances. 



The teeth, as shown in the figure, appear to have been uni- 

 formly directed backwards and inwards, and the lowest row 

 in the series lies quite flat, as in the recent genera Galeus, 

 Carcharias, &c. A circumstance worth notice is that the 

 lowest row in the series is shown, by fractured specimens, to 

 be fully as capable of taking office as those occupying the 

 front rank; now the corresponding teeth in many existing 

 squaloid genera are mere hollow cases, which become gradu- 

 ally filled with osseous matter as they ascend in the series. 



I have been led rather minutely to detail the characters 

 presented by this fossil jaw, because so large a number of 

 species are included in the genus, and also because I have 

 not been able to refer it to any species hitherto described. — 

 Agassiz has figured the teeth of three species of Hybodus 

 from the lias of Lyme Regis and Bristol, namely, Hyb. rari- 

 costatus, reticulatus, and medius. The teeth of the present 

 species differ from the first of these in the greater size of the 

 central process, and the less distinct development of the la- 

 teral ones, and in presenting much more numerous and small- 



1 The divergence of these lines is "best shown hy the recumhent teeth 

 about the middle of the anterior border of the larger fragment, (fig. 1). 



