1848. ] SIR P. EGERTON ON PTERICHTHYS. 313 
specimen of Cheiracanthus. Figs. 2, 3 & 4 all give the same view. 
In figs. 2 & 3 a dorsal plate is seen dislocated. 
PTERICHTHYS CORNUTUS. Tab. 2. 
Figs. 1 & 2 represent a beautiful little specimen, one part of which 
is at Florence Court, the other at Altyre. The artist however has 
reversed the fish. When looked at in its proper position it gives a 
very tolerable idea of the outline of Pterichthys seen in profile. 
Figs. 4 & 5 show the under surface. The horn-like protuberances in 
the former appear to indicate the position of the glenoid cavity for 
the reception of the articulating head of the pectoral fin. » The dorsal 
plate in this species is very large ; in a specimen of which the cara- 
pace measures 21 inches it occupies more than 1+ of the surface. 
PTERICHTHYS OBLONGUS. ‘Tab. 3. figs. 1 & 2. 
Both figures show the inferior surface. In addition to the cha- 
racters assigned by Agassiz to this species may be mentioned that 
the pectoral fins are covered anteriorly with strong tubercles (in sec- 
tion they almost resemble the teeth of Coccosteus), and the scales are 
ornamented in like manner. 
New Species. 
PTERICHTHYS QUADRATUS, Egerton. Plate X. 
On looking over a large collection of Gamrie nodules I found that 
many of the specimens of Pterichthys indicated a larger and broader 
fish than the common species of that locality, P. oblongus.. On com- 
paring these specimens with the Lethen and Cromartie species it was 
evident they were not the remains of any species yet noticed. The 
best specimen shows the ventral plates im situ. ‘This surface was 
shorter and broader than the corresponding part in P. Jatus, which 
it most resembles. ‘The rounded form and large size of the central 
plate are characters common to the two species, and eliminating both 
from the other species of the genus. The most marked distinctions 
between them are found in the form of the posterior ventral plates 
and the ornament of the carapace. In P. quadratus these plates 
contract rapidly in diameter as they recede from the middle lateral 
plates, and terminate posteriorly in an angular form, in contradistinc- 
tion to the corresponding plates in P. latus, which are broad and 
rounded. ‘The ornament of the carapace is not coarse and confluent as 
in P. latus, but more like P. oblongus. The tubercles are granular 
_ or arenate, and arranged rather irregularly. They are not uniform in 
size, but all small and distinct from each other. The central dorsal 
plate is not proportionally so large as in P. cornutus, nor is thé apex 
so acute. The pectoral fins were strong, and covered with rugged 
tubercles. This species appears to have been nearly as common as 
P.oblongus. In the collection of the Society I have recently found 
a most beautiful specimen of this species, indeed altogether the most 
instructive and interesting example of the genus Pterichthys I have 
ever seen. The fish reposes on its back, and by a fortunate accident 
