518 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
large rounded glands lying beside the ventral part of the ovary. 
Their efferent ducts unite to form a common sperm duct running 
along beside the ovary and apparently reaching nearly to the dorsal 
end of that organ. 
This is a deep-sea species not properly belonging to the New Eng- 
land fauna. The only specimen was dredged in the deep water off 
the eastern edge of George's Bank at Station 2572 (N. lat. 40° 29', 
W. long. 66° 04', 1769 fathoms, gray ooze). 
Caesira singularis, sp. nov. 
Pi. 54, fig. 58-60; PI. 73, fig. 166; text-fig.s. 21, 22. 
In its external appearance this species resembles a small Caesira 
arcnata (Stimpson), having the same general form, though the body 
appears to average a trifle longer in proportion to its depth and to be 
usually less compressed laterally. As in Caesira arcnaia the apertures 
are widely separated and the sui'face of the body is completely covered 
Text-flg. 21. — Caesira singularis, sp. nov. X 4. 
with sand. The apertures were so tightly contracted in the specimens 
studied that the lobes surrounding them could not be satisfactorily 
counted either from the outside or on the mantle after removal from 
test. The test is rather thin yet of firm, more or less rigid consis- 
tency; its interior surface when dry exliibits a whitish, somewhat 
nacreous luster. The largest specimen measures 11.5 mm. long, 
9 mm. dorsoventrally, and 7 mm. from side to side. 
After removing the animal from the test there is, however, no more 
occasion for confusing this species with C. arcnata. The mantle is 
very thin and transparent, so that the peculiar form of the gonads is 
readily visible through it, and the musculature of the mantle is likewise 
totally different from that of the last named species, consisting of a 
