tio. 1848. RECENT CLADOCERA FROM NEW ENGLAND— DOOLITTLE. 167 



cells lateral to it there radiate to the facial ridges a number of parti- 

 tions further dividing the facial area into long radiating cells, some- 

 what rectangular in form and corresponding in nimiber to the cells 

 external to the facial ridges. Immediately ventral to the ocular cell 

 there are four cells, behind whose common meeting point is the 

 macula nigra or ocellus. To the tip of the rostrum there nm the 

 ridges already referred to and a convergmg series of elongated cells 

 diminisliing in height distally. 



Each valve of the test supports four prominent ridges below the 

 horn, some especially conspicuous from front and from dorsal view. 

 Those of each side have their origin very near each other at the upper 

 end of the anterior border of the test. Their general direction is 

 parallel to the ventral edge, two of them upon or near the margin, 

 and tv.'o a Uttle removed from the margin. They will be called, 

 taldng them in order from the margin, the marginal, submarginal, 

 inferior valval, and superior valval ridges. The superior valval ridge 

 standing out at right angles to the test is a very conspicuous object 

 in front view, and also from dorsal view its posterior part, wliich is 

 seen to end one-fourth from the posterior end of test. The submar- 

 ginal ridge takes its origin where the inferior spinal ridge is lost 

 among the hexagonal cells at the upper end of the anterior margin of 

 the valve, crosses the origms of the valval ridges, and merges with 

 the marginal ridge midventrally. The inferior valval ridge and the 

 marginal ridge follow the directions already indicated for them, and 

 parallel to those just discussed, and fuse opposite the superior angle 

 of the posterior margin as the margino-valval ridge. At tliis point 

 it flares outward sUghtly and running forward on the back joins the 

 posterior interspinal ridge. The space thus inclosed between these 

 miited ridges of each side is the posterior dorsal area. Across the 

 anterior end of the area are three large cells. The remaining part of 

 the area is open. The portion of the valves included between the 

 two clefts and the valval ridges is filled with hexagonal cells, larger 

 dorsally and posteriorly and smaller anteriorly. From ridge to adja- 

 cent parallel ridge high partitions pass, dividing the intervening space 

 into deep rectangidar cells. 



Rostrum long, acute, often included between the ridges upon the 

 anterior margins of the valves; the anterior portion of the superior 

 spinal ridge forms a sort of fornix across its base. Eye large; ocellus 

 one-half its diameter, in the base of rostrum. Antennules slender, 

 failing to reach tip of rostrum by about their length; sensor}^ seta in 

 angle upon anterior margin distally; five or more subequal, short, 

 olfactory setae apically. Antennae short, not reachmg to end of 

 antennules. Rami with setae ^f|, with spines m; one of the cUstal 

 setae of lower or inner ramus one-third the length of the remaining. 

 Labrum from side view with short, bhmt anterior lobe, and elongated, 

 fingerhke, posterior lobe, dii^ected ventro-posteriorly, tipped with 



