140 University of California Puhlications. [^^^ology 



is short, broad, and truncated anteriorly; rostral sinus shallow, 

 widely open forwards and downwards. The surface of the valves 

 is everywhere pitted with round, oval, or quadrangular foveolae 

 which vary somewhat in size ; marginal hairs located chiefly along 

 anterior and posterior margins. Transparent margin of shell 

 rather broad and thickly fringed with cilia. 



The first joint of the antennule bears no setae ; second joint 

 longer than first, about as long as the rest of the limb, bearing 

 three setae toward the distal end which are plumose in the mid- 

 dle ; this joint also has some very minute marginal spines ; third 

 joint sub-triangular, with two naked setae on the inner margin 

 and one on the outer ; fourth with two distal setae on the inner 

 margin and four on the outer, two of the latter setae being- naked 

 and the other four more or less plumose in the middle ; the fourth 

 joint also possesses a rather large sensory seta on its outer margin 

 which bears a tuft of hair-like processes on its basal fourth and 

 divides into four small branches at its outer extremity ; fifth joint 

 with only a naked seta on its inner margin ; sixth with two very 

 long" setae which are reflexed upon the limb and which bear a few 

 hair-like processes ; in addition, the sixth bears five much shorter 

 setae, two of which are rather stout, possess some hair-like pro- 

 cesses in the middle, and branch at the outer end ; the other three 

 are slender, unarmed, and not branched at the extremity. 



The second joint of the swimming branch of the antenna bears 

 a long naked seta at its distal end which reaches as far as the 

 sixth or seventh joint ; third joint longer than second and bearing 

 a plumose swimming seta at its distal end ; the remaining joints 

 are short and bear ten plumose swimming setae. The first joint 

 of the secondary branch of the antenna is a little longer than wide 

 and bears a cluster of five small setae on its proximal end, just 

 beyond these is a longer seta which is plumose in the middle; 

 second joint long and slender, with two, sometimes three, annul- 

 ated setae; third joint about three-fourths as long as the second 

 and reflexed upon it ; this joint consists of a rather large cone- 

 shaped base and a slenderer, curved portion ; the outer end has a 

 few crenulations and bears two, sometimes three, small setae ; the 

 basal portion of the third joint bears a very long, peculiar seta ; 

 the proximal half of this seta is large and has thin walls similar 



