34 FOSSIL MALACOSTRACOUS CRUSTACEA. 



cephalic portion of the carapace ; there are on this part seven more or less distinct carinae, 

 three pairs and one on the median line ; the lowest is short, and extends backwards along 

 the side of the scapular arch, being interrnptcd only by the nuchal furrow; the next 

 above it is strongly marked, acute, and, like the former, has a series of small tubercles ; it 

 extends forwards to a minute superorbitar spine ; the median carina extends from a 

 short distance in front of the nuchal furrow nearly to the rostrum, and two others, con- 

 verging regularly, terminate at its apex. The scapular arch or portion of the carapace 

 behind the nuchal furrow has a strongly raised median carina, another on each side con- 

 tinuous with the second on the anterior portion, and between these is an awl-shaped 

 elevation, passing backwards and upwards, and, like the former, tuberculated. The whole 

 surface is granulated, though more sparsely than in 3f. ornata. The abdomen is more 

 compressed than in that species ; the segments are somewhat longer, and have three small 

 longitudinal carina?, each of which is furnished M'ith a series of a few granulations. The 

 lateral or epimeral processes are irregularly sculj)tured, and have a few scattered granu- 

 lations. The lateral pieces of the tail have each a longitudinal carina, and the exterior 

 one shows very distinctly the transverse division which denotes its relation to the Astacoid 

 group. The legs are long, slender, and compressed, and the first (?) pair, which is 

 extremely long, is angular and carinated, and has several longitudinal rows of small spines. 

 .Judging from the fragments which I have had an opportunity of examining, this extraor- 

 dinary development of the leg may depend on sex, as the portion which remains of this 

 limb in some specimens appears to be much smaller than in others. The second pair is 

 also much larger than the remaining ones. The kilter are nearly smooth, and evenly 

 compressed, without any angularity. 



Length of carapace 2'5 inches, height 1'2 inch; length of abdomen 3-5 inches. 



From the Greensand at Atherfield, in the Isle of AVight, where it occurs in profusion, 

 so as to have given to the beds where it is found the name of " Lobster beds" — M'Coy 

 also gives " Speeton clay of Speetou" as another locality, but I have not met with any 

 specimens from thence, and am doubtful of the correctness of this statement. 



Geaus — Pulyctisoma, Bell. 



Char. Gen. Testa tuberculata, lobo mesogastrieo distincto, separato, lineari. Abdomen 

 semicylindricum, epimeris elongatis, angustis. Pedes antici robusti, tumidi, tuberculati ; 

 reliqui la)vis, compressi. 



