MUSEUM OF COMPARATIVE ZOOLOGY. 29 



thickness of tlie propodus, or a little longer, slender, and tapers to a rounded 

 tip, while the dactylus is nearly or fully twice as long, considerably stouter, 

 straight, and nearly cylindrical. In the female (fig. 12) the propodal digit 

 is scarcely as long as in the male, is more slender, and tapers to an acute 

 and incurved tip, which is somewhat flattened and excavated on the anterior 

 and inner side, leaving an edge on the posterior side ; the dactylus reaches 

 very nearly to the tip of the propodal digit, and is like it in form, Lut a little 

 more sharply incurved at tip. 



The branchiae resemble the branchife of the Astacida;, being slender, very 

 soft, and composed of slender filaments, which are not closely crowded together. 

 There are no branchiae connected with the first and second maxillipeds, but 

 above the base of the third maxilliped and between the lameUar epipod of 

 the first maxilliped and the coxa of the first leg there is a slight lamellar ele- 

 vation bearing a few filaments which are apparently branchial and may repre- 

 sent a very rudimentary epipodal branchia. The legs of the first four pairs 

 bear each a well-developed podobranchia and a small epipodal plate, lying 

 just at the edge of the carapax but not projecting into the branchial chamber, 

 and above the bases of each of these legs there are two arthrobranchise and one 

 pleurobranchia. There is also a pleurobranchia above the base of the fifth leg, 

 80 that there are in all sixteen well-developed branchia, — four podobranchia;, 

 eight arthrobranchise, and four pleurobranchise each side, as indicated in the 

 following formula : — 



Somites. VIT. VIII. 



Epipods, 



Podobranchife, 



Arthrobranchise, 



Pleurobranchise, 



16+(5) 



As seen from above, the sides of the abdomen are nearly straight, and form, 

 with the telson, a regular acute triangle. The first five somites are carinated 

 dorsally, and the carina projects forward from each somite in an acute tooth, 

 but the carina and tooth are small and low on the first somite, increase rapidly 

 to the fourth, while on the fifth they are scarcely as prominent as on the fourth, 

 and on the sixth the carina is inconspicuous and there is no tooth, but the top 

 of the carina is traversed by a narrow longitudinal sulcus. On the first somite 

 there are, in addition, two slender spines each side projecting forward above 

 the articulations with the carapax. The dorsal surface of the abdomen, either 

 side of the median carina, is smooth and scarcely at all sculptured ; but along 

 the lateral margin, where the pleura bend abruptly and nearly perpendicularly 

 downward, there is a series of deep longitudinal sulci, except upon the narrow 

 first somite, which is unsculptured, and upon the sixth, where the sulcus is 

 replaced by a simple carina. Of the pleura themselves, the first is nearly obso- 

 lete, the second is broader than deep, projecting back over the third with a 

 broadly rounded margin, and forward in a prominent but rounded angle, and 



