T erminal claws long and slender, with a row of fine teeth, on each 

 side. Teeth of equal size in each row. Macula nigra rhom- 

 boidal. 



The head is separated from the body by an obvious depression. 

 Its upper margin curves pretty regularly downward to the. point 

 where the fornices approach it more closely, where it bends down- 

 ward abruptly, and after a short distance is bent again, so as to 

 form almost an acute angle with the front margin. At this angle 

 are three or more short teeth. The fornices project considerably. 

 The superior margin of the valves is arched, serrate, and produced 

 into a short spine behind. In old animals the back is so much 

 arched as to bring the spine near the middle of the hinder edge. 

 In the young it is near the top of the hinder edge. The posterior 

 and part of the ventral margins are serrate. The anterior margin 

 is concave. The valves have the markings characteristic of the 

 genus. The abdomen has two blunt, weak processes. 



The post-abdomen is broad, compressed and truncate. Its 

 greatest width at the top is often greater than its length to the in- 

 sertion of the terminal claws. These are long and slender, with a 

 row of fine teeth on each side. The teeth are of equal size in both 

 rows, and are about 0.01 mm. long. There are eight or nine cau- 

 dal teeth in each row, geniculate, and bearing a row of fine setae. 

 Besides these, there are often five or six other very fine teeth, 

 completing the row across the post-abdomen. 



The antennules are freely movable, slightly curved, shaped like 

 a truncated cone, and ornamented with several short cross rows 

 of fine teeth. The antennae and their branches bear the same or- 

 nament, and on the basal joint are a pair of short, two-jointed 

 setae, projecting upward from a slight elevation, and a similar seta 

 near the insertion of the branches. 



The macula nigra, as seen from the side, is rhomboidal, with 

 the upper angle sometimes a little prolonged. 



A rudimentary haft-organ is found in young animals, bat dis- 

 appears in the adults. 



The male resembles in general the young female. The testicle 

 is very large, extending the whole length of the body. The vasa 

 deferentia open on both sides of the post-abdomen, at the angle 



