144 University of California Publications. [Zoology 



the sensory organ consists of a stont annnlatecl base which bears 

 numerons fine thread-like processes; the sixth joint bears three 

 short and two very long setae. Antenna with the second joint of 

 the natatory branch about as long as three of the following- joints ; 

 secondary branch of antenna three-jointed, rather large and 

 strong ; first joint uniform in width, about four times as long as 

 wide; second about as long as first, dilated on the side against 

 which the last joint impinges, and bearing three setae just be- 

 yond the middle ; third joint falcate, slender, about three-fourths 

 as long as second, and reflexed upon it, forming a grasping organ ; 

 with a few serrations on its inner margin at the extremity and a 

 seta near the proximal end. 



The first maxilla consists of a lobe-like body portion and two 

 acuminate arms; the smaller arm is straight and bears no setae; 

 the outer portion of the other arm is bent around toward the 

 body, forming a bow ; the outer margin of the bow bears only two 

 small setae and there are two at the extremity of the arm; the 

 inner margin, except a small portion at the extremity, is densely 

 fringed with long, slender setae. The vermiform limb bears six 

 setae at its extremity and six on the sides. The furca bears ten 

 claws; the upper five small, the lower five increasing in length 

 and pectinated as well as ciliated. 



Length 1.4; height 0.75 mm. 



Female. — Shell in side view nearly oblong, dorsal and ventral 

 margins scarcely arched in the middle, nearly straight ; these mar- 

 gins curve over gradually into the anterior and the posterior. 

 Antennal sinus narrow and deep, situated below middle of ante- 

 rior margin. In both sexes the valves are strongly calcareous, 

 smooth, and bear a few cilia along the anterior margin. 



The sensory organ of the fourth joint of the antennule con- 

 sists of an annulated basal portion which flattens out and divides 

 into six thong-like processes ; the sixth joint bears five setae which 

 are about equal in length. Second joint of natatory branch of 

 antenna scarcely as long as the two following joints; secondary 

 branch of antenna three-jointed, the last joint being indistinctly 

 separated from the second ; the last joint bears a rather long seta. 

 The arm-like projection of the second maxilla is twisted half way 

 round in the female, but not twisted in the male. 



