On a new Astacamorphous Crustacean, from the Middle Coral 
Reef of Leckhampton Hill. By Dr. Tos. Wricut, F.R.S., 
F.G.S., &e. 
The Astacina form a small interesting group of the Deca- 
podous Crustacea, which are well represented by the common 
Cray-fish (Astacus fluviatilis) so abundant in some of the rivulets 
of the Cotteswold Hills. 
The genus Astacus has the external skeleton partly calca- 
reous and partly membranous; the cephalothorax large, and 
compressed on the sides; the post abdomen flattened; the 
plastron small and linear; the rostrum a prominent spear- 
pointed projection; the external pair of antenne long, filiform, 
and annulated like a whip-lash; supported on short round stems, 
making a complete structure two-thirds the length of the entire 
animal; at the external side of the antenne is a sabre-like scale 
attached to the stem; the internal antennules are very short, the 
two on each shaft are small filiform annulated processes which 
lie above and external to the long antenne. The two eyes 
project beyond the rostrum, each is seated on a moveable stalk, 
wider at the base, which readily turns the eye in all directions. 
The first pair of feet are weapons of offence and defence; they 
are strong instruments, and terminate in a pair of didactyle 
chele, forming forceps, which they use dextrously and with a 
good deal of disposable energy. The 2nd and 38rd pairs of 
ambulatory feet are much more slender, and they likewise 
terminate ina pair of small weak forceps. The 4th and 5th 
ambulatory feet are about the same thickness, but much 
shorter, and terminate in short pointed claws. The abdomen 
consists of six rings or somites; the upper half (tergwm) of 
each somite is arched and shield-like, with two lateral wing- 
like projections (plewra); the lower half (sternum) is flat 
and more membranous, and in the female develops a pair of 
swimmerets attached to the five anterior rings. Behind the 
