20 G. O. Sars. 
front of the median prominence the edges are clothed with 
delicate bristles, and just within the margin a cellular stra- 
tum occurs similar to that found in other species. I have, 
however, failed to detect on the valves any trace of the 
usual irregular siriation. 
The head is comparatively small and, seen laterally 
(fig. 1), of a somewhat triangular outline. It is remarkably 
erect, not, as in the other known species, procumbent, and 
has the frontal part rather prominent and narrowly rounded 
at the tip, with only a very slight indication of a sinus 
above. The ventral margin of the head is nearly straight 
and horizontal, being continuous with the labrum; the dorsal 
margin. appears slightly vaulted. Seen from above (fig. 2), 
the head appears rather broad, subpentagonal in form, with 
the greatest width about equalling the height, and the front 
obtusely rounded, The fornix is well defined, though not 
very prominent, and occurs just above the base of the oars. 
The eye, occurring just within the frontal part, is not 
particularly large, exhibiting, however, the usual structure. 
As in the other species, no trace of an ocellus is to be 
detected. 
The antennulæ (fig. 3) equal about half the length of 
the head. They are, as in the other species, freely mobile 
and of a subfusiform shape, with the posterior edge finely 
ciliated. The sensory bristle of the anterior edge occurs 
about in the middle. The apical olfactory papille are very 
small. 
The antenne or oars (see figs. 1 & 2) are powerfully 
developed, and agree in their structure exactly with those 
in the other species of the genus. At their base exteriorly 
2 remarkably large, juxtaposed setæ occur pointing straight 
outwards. 
