THE FOSSIL STALK-EYED CRUSTACEA 131 



orbicular, anterior and posterior margins broadly arcuate, postero- 

 external portion outwardly produced ; this pleuron is about one and 

 a half times as long (in the direction of the axis of the crayfish) as 

 the greatest length (in the same direction) of any of the next three 

 pleura. The third, fourth and fifth somites are of subequal length, 

 their pleura similar, falcate, each extending laterally a distance equal 

 to that between articulations. The sixth somite is about the same 

 length as those preceding, but its pleuron is subtriangular, about half 

 as extensive and directed obliquely backward. The telson (pi. 32, 

 fig. 2) is about seven-eighths as wide at its origin as its length; its 

 lateral margins converge slightly in the proximal half, strongly in 

 the distal half, the extremity broadly arcuate ; the lateral incision is 

 at the distal two-fifths of the length. The branches of the tail-fan 

 are broadly oblong-oval; when longitudinally disposed the inner 

 branch exceeds the telson very slightly while the outer one is con- 

 siderably longer ; the transverse suture of the outer branch is almost 

 in line with (a little in advance of) the posterior end of the telson, 

 and is marked by a row of spines and spinules. 



Chelipeds : Unequal, asymmetrical, one chela (either right or left) 

 longer and slenderer than the other. The first is the chenoderma 

 type, the second the hreviforceps type. Surface rougher than that 

 of the body. Merus (pi. 33, fig. 2) twice as long as its gi-eatest 

 width, margins tuberculate; upper margin with a single row of 

 tubercles ending in a cluster of tubercles just behind the transverse 

 distal furrow; a row of tubercles on either margin of the narrow 

 lower surface, and on the distal margin, ending in a cluster of tuber- 

 cles at the outer angle. Carpus (pi. 31, fig. 5) with a deep longi- 

 tudinal furrow in its upper surface, the portion outside the furrow 

 very coarsely and roughly tuberculate. Palm of major chela (pi. 

 31, fig. 5) as wide as its length between articulations with carpus 

 and dactylus; palm of minor chela (pi. 31, fig. 2) somewhat nar- 

 rower than its length between articulations. Their outer or upper 

 surface is rougher than the inner or lower one and the tubercles are 

 larger and more abundant toward the margins where the sockets 

 with which they are provided probably supported a coating of soft 

 hair. The fingers are long and flattened, longer in the minor chela 

 (pi. 31, fig. 3). In the minor chela the outer edge of the dactjdus 

 or movable finger is concave, and the opposite or prehensile edge is 

 slightly convex; the outer edge of the immovable finger is convex 

 and the prehensile edge concave; the fingers therefore meet when 

 closed. In the major chela the prehensile edges of both fingers are 

 somewhat concave and the outer edges convex, resulting in a narrow 

 interspace at least in the proximal half when the fingers are closed 

 (pi. 31, fig. 5). 



