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 diyerge,' and,spreading oyer.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.oceupied, 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 ina 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 inthe 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, Hyd. 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- 
UThe divergence of these lines. is, best) shown by the recumbent teeth 
about the middle of the anterior border of the larger fragment, (fig. 1): 
