MUSEUM OF COMPAKATIVE ZOOLOGY. 47 



The sternum is flat, triangular, and wholly unarmed. 



The abdomen is about once and a half as long as the carapax including the 

 rostrum, is narrower than the carapax, and as seen from above tapers regularly 

 from the base to the tip of the telson. There is a sharp medio-dorsal carina 

 from the base to the telson, but interrupted on all the somites but the first ; a 

 single lateral carina each side is indistinctly indicated on the first two or three 

 somites ; and the dorsal surface generally is studded with prominent tubercles, 

 many of which are elongated and all the larger ones with flattened and punc- 

 tate tops. Upon the first somite, the median carina is thin and very high and 

 projects forward in an acute tooth ; either side, in line with the upper lateral 

 carina of the carapax, there is a very prominent acute and spinifonn tooth 

 directed obliquely forward. On the second and third somites, the dorsal carina 

 is divided into two nearly equal parts by a smooth and very conspicuous sulcus, 

 which passes slightly backward either side across the whole dorsum of the 

 segment and down parallel with and near to the posterior margin of the epim- 

 eron ; the anterior part of the carina on the second somite is nearly as high 

 as on the first and projects slightly forward, but the posterior part on the second 

 and both parts on the third are much lower and do not project in front or be- 

 hind. On the fourth somite, the carina is divided into two unequal parts by a 

 less conspicuous sulcus, the anterior part being like that upon the third somite, 

 while the posterior part is twice as long, thickened and flat above anteriorlv, 

 but posteriorly higher, more acute, and projecting slightly over the fifth somite. 

 On the fifth somite the carina is unequally divided by a similar sulcus, but the 

 anterior portion is more prominent than on the fourth, and the posterior part 

 is very prominent, its anterior half being formed of two longitudinally elon- 

 gated tubercles slightly diverging posteriorly, and between and back of them 

 a single very high sharp and triangular tooth. The carina upon the sixth 

 somite is broken anteriorly by a small notch, and posteriorly rises in an acute 

 edge and projects far back over the base of the telson in an acute tooth. The 

 epimeron of the first somite is narrow, does not project below the margin of the 

 carapax, is rounded below and almost wholly covered by the anterior expansion 

 of the epimeron of the second somite when the abdomen is fully flexed. The 

 epimeron of the second somite projects much below the epimeron of the Gist, 

 the anterior margin is nearly as convex in outline as the posterior, the inferior 

 margin projects in the middle in a very long, slender, and outcurved spine, in 

 a much smaller spine at the posterior angle, and in a small tooth anteriorly ; 

 on the outer surface a sulcus, like and nearly parallel with the sulcus of the 

 porterior border, passes from near the anterior binge to the base of die large 

 spine of the inferior margin, but between and outside o( the sulci the surface is 

 sparsely tuberculous. The epimera of the third, fourth, and fifth somites have 

 a smooth depressed area along the anterior margin, and are each armed below 

 with two slender acute and out-curved spines, of which the anterior one on each 

 epimeron is about as long as the large spine of the second epimeron. while the 

 posterior spines increase in length from the second to the fifth somite, that 

 upon the fifth epimeron being longer than the anterior spine o\' the 



