PYCXODONTIDiE. 
239 
depth of trunk somewhat less than its length from the scapular 
arch to the base of the caudal fin, and head with opercular 
apparatus occupying less than one-third of the total length ex¬ 
clusive of the caudal fin. External head-bones ornamented with 
tuberculationS. Dentition closely arranged, with comparativelv 
feeble ornament, soon worn smooth. Yomer with prominent flat- 
topped median teeth, higher than either of the flanking series, and 
equalling or exceeding these two series together in width ; the 
inner flanking series somewhat smaller than the outer, of which the 
teeth are not much elevated. Splenial with principal teeth broader 
than long, about equalling in width the two flanking series, of which 
the outermost is much the largest; inner flanking teeth equalling in 
size those of the innermost series. Dorsal fin occupying the hinder 
half of the back, and its maximum elevation equalling at least one 
third of the depth of the trunk at its insertion. Scales towards the 
dorsal margin ornamented with distant tubercles, the others marked 
with a delicate reticulation, partly also tuberculated. 
Form. Loc. Lower Kimmeridgian (Lithographic Stone): Bavaria 
and Wiirtemberg. 
49146. Plaster cast of type specimen, the head figured by Wagner. 
loc. cit. 1851, pi. i. fig. 1; Solenhofen, Bavaria. 
Purchased , 1878. 
37039. A fine specimen 0*68 in length, with imperfect head and 
paired fins : Solenhofen. Hdberlein Coll. 
37792. Head with imperfect trunk and dorsal fin of a still larger 
fish; Solenhofen. The mouth is open, and the worn 
vomerine and splenial dentition has been well extricated 
from the matrix. Two of the anterior prehensile teeth of 
the lower jaw and one in the upper jaw are also shown. 
Some of the small, coarsely tuberculated scales are shown 
below the hinder part of the mandible. Hdberlein Coll, 
P. 1622. Eragment of squamation ; Solenhofen. Egerton Coll. 
P. 3775. Smaller fragment; Daiting, Bavaria. Ennislcillen Coll. 
35532. Plaster cast of vomerine dentition probably of this species, 
described and figured by Count von Mandelslohe, loc. cit. 
1845 ; Wippingen, near Blaubeuren, Wiirtemberg. 
Purchased, 1859. 
It is not improbable that to Gyrodus circidaris must also be 
assigned the portions of dentition named Gyrodus umbilicus (L. 
