112 
DAVIS : NOTE ON CHLAMYDOSELACIIUS. 
those of C. curvus. The base is large and tiiick, extending- back- 
ward with a slig-ht obhquity (op. cit., 16). So far as the writer 
is aware, amongst British species the one or the other of the two 
last named appears to approach most nearly in external form 
to the teeth described by Mr. Garman. The author has referred to 
the American genera Pternodus (Pristicladodus, St. John and 
Worthen) and Trinacodus, St. J. and W., both from the Kinderhook 
fish beds, and more or less allied to the genus Cladodus (see 
Oeological Survey of Illinois, Vol. YI.), and suggests that they 
may constitute an intermediate link between the form of Cladodus 
and the new genus. 
There is then on the one hand the fossil teeth having a 
horizontal base with rounded posterior margin and erect denticles 
three or more in number ; and on the other, the existing shark with 
teeth of varied forms, the more important of which have a broad 
base, whose posterior margin is prolonged into a pair of prongs 
which extend beneath the contiguous tooth. Three denticles spring 
from the anterior part of the base, equal in size, and bent backwards 
over the base with which they form a more or less acute angle. 
These teeth differ greatly from the type of Cladodus mirahiliff^ 
Agass., but others occupying a position more remote from the 
symphysis of the jaws have a different form, the denticles, three in 
number, are erect, and the lateral ones are smaller than the one in 
the middle ; the resemblance in this instance is very close to the 
teeth of the fossil Cladodus, but again, other teeth still more remote 
lose the lateral or secondary denticles and have only a single median 
cusp. 
^ur knowledge of the fossil forms of Cladodus does not lead us 
to infer that the teeth of Cladodus differed in form to any extent 
comparable with those of the existing Chlamydoselachus. There 
are no fossil examples known to be associated with the ordinary 
form of Cladodus similar to those of either the anterior recurved 
teeth or the posterior ones with a single denticle as in the recent 
fish, and the question naturally arises as to whether the correspond- 
ence in the form of one portion of the teeth of Chlamydoselachus is 
sufficient to justify the assumption that the latter is the existing 
