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Mr. J. W. Davis on a new Species of Ptycholepis. 337 
to the outer extremity of the rays. A series of minute fulcral 
scales extends along the margin of the anterior ray of the fin. 
The ventral jin is smaller than the pectoral and is equidistant 
between the pectoral fin and the tail; in this specimen the 
fin may not be quite perfect; it is °7 inch in length. The 
basal part of the rays is grooved longitudinally, as in the 
pectoral fin, and their extremities are divided into two or 
more parts. The anal fin is not well defined. The tazd is 
supported by a base *7 inch across; it is forked, the distal 
extremities of the two lobes being 2 inches apart. The base 
of each lobe is somewhat hidden by a covering of iron pyrites ; 
the extremities are composed of fine rays divided and sub- 
divided from those nearer the base; each is composed of 
numerous small joints attached by transverse articulations. 
A number of triangular scales thickly coated with black 
enamel encircle the dorsal aspect of the base of the tail and 
extend along the margin of the upper lobe of the tail in an 
oblique imbricating series, decreasing in size as they approach 
the extremity. The lower lobe is devoid of fulcra. The 
vertebral column is extended towards or partially into the 
upper lobe of the tail. The lower lobe, though the rays are 
finer, is considerably larger than the upper one. 
This species is characterized by its slim and graceful form 
and the small size of the head in proportion to that of the 
body. It may also be distinguished by the ornamentation of 
the head-plates and scales, the difference between the latter 
and the corresponding scales of the species described by Prof. 
Agassiz and Sir Philip Egerton being sufficiently character- 
istic. Sir Philip Egerton, ina supplement to the eighth decade 
of the ‘ Memoirs of the Geological Survey,’ gives some details 
of a second specimen of Ptycholepis curtus found at Lyme 
Regis ; the length of the fish is 5} inches and that of the 
head two inches, showing a similar disproportion as compared 
with the example now described. The ventral fins are placed 
nearer to the pectoral than the anal fins in P. curtus; whereas 
in this species the anal fin cannot be more than half as far 
from the ventral as the latter from the pectoral. 
I propose to designate this species Ptycholepis gracilis, 
Locality. Lias, Lyme Regis. 
EXPLANATION OF PLATE X. 
Fig. 1. Ptycholepis gracilis, Davis. Natural size. 
Fig. 1a. Scale midway across the body, about half an inch behind the 
operculum, X15, 
Fig. 16. Scale near the caudal extremity. x 15. 
Fig. 1c. Scale from the ventral surface. x 15. 
