176 Prof. F. M‘Coy on the Classification of 
and smooth, or with few very minute teeth ; beneath the orbits 
the cheeks are prolonged forwards about half the length of the 
rostrum, and usually strongly keeled and spinose, forming a 
semicylindrical sheath over the base of the strong triangular 
scale of the origin of the outer antennz, which reaches 
as far as the rostrum ; nuchal furrow strongly marked across 
the middle of the back, but not reaching the marginal third 
of each side; cheeks* impressed by a deep A-shaped sulcus, 
one portion of which extends upwards nearly parallel with the 
nuchal furrow, the longer lower branch curves forward under 
the projecting part of the cheeks, and the shorter branch 
curves backwards under the end of the nuchal furrow ; abdo- 
men subcylindrical, smooth or slightly punctured, the second 
joint having broad, dilated quadrate ends, the third, fourth, 
and fifth terminating in triangular or broadly falcate extre- 
mities, the sixth having articulated to each end the two outer 
pairs of large trigonal tail-fins, the outer one on each side divided 
by a transverse suture rather less than one-third from the ex- 
tremity ; seventh joint (or middle flap of the tail) oblong, sides 
denticulated, extremity narrower than the base, and bearing a 
small spine at each corner ; first pair of legs very long and 
thick, unequal, the larger claw with large blunt teeth, the 
more slender one with more numerous and equal smaller sharp 
teeth ; the other legs slender. 
In the general characters, so far as I have been able to ascer- 
tain them, these crustaceans coincide with the hving genus Ho- 
marus, but are constantly distinguished by the sheath-like pro- 
longation of the strongly ridged and spinose cheeks, the nearly 
smooth-sided rostrum, and the short distance which the nuchal 
furrow extends down the sides, as well as the separate A-shaped 
cheek-furrow on each side, and the size of the antennary scale. 
There are several species common in the British eocene tertiary 
and eretaceous rocks, only one of which has yet been noticed, 
viz. the Astacus longimanus of G. Sowerby (Zoological Journal, 
vol. ii. tab. 17) from the greensand of Lyme Regis, which I find 
to belong to the present genus, and which should have the name 
Hoploparia longimana (Sow. sp.). 
Hoploparia prismatica (M‘Coy). 
Sp. Char. Carapace (excluding the rostrum) 1} inch long, width 
10 lines, subeylindrical behind, but having the section of 
a five-sided prism towards the front from the strong pro- 
jection of the large, acutely angular cheek-ridges, which bear 4 
* Or sides of the carapace immediately in front of each end of the nuchal 
furrow. 
Ra 
