148 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
LED A TENUISULCATA (Couthouy). 
Fig. 4. Length, 25 mm. 
The only drawing I succeeded in getting of this species shows 
two very short syphons united, the branchial orifice plain, the 
anal orifice faintly notched. A lobe of the mantle projects just 
below the syphons with its free edge irregular, and in line with 
the lappet appear two thread-like appendages extending far 
beyond the ends of the syphons. Whether these are thread-like 
palpi, which seems impossible, or represent a double syphonal 
Fig. 4. — Leda tenuisulcata (Couthouy). 
tentacle is yet to be determined. At the base of the anterior 
edge of the shell the mantle supports on each side a wart-like 
excrescence which Drew regards as a sense organ. He says these 
tubercles are very sensitive to mechanical stimulation and prob- 
ably serve as tactile organs. They are more prominently devel- 
oped in Yoldia as we shall presently see. The foot is sharp, 
angular, with pectinated edges, and probably expands in swim- 
ming as in Yoldia. 
YOLDIA SAPOTILLA (Gould), 
Fig. 5. Length, 21 mm. 
The mantle projects beyond the posterior end of the shell 
forming a collar embracing the base of the syphons. The edge 
of this collar is shghtly reflected with irregular outline. Just 
below this is a distinct lobe of the mantle rounded in form and 
fringed with large papillae of varying sizes and these papillae 
continue along the ventral edge of the mantle nearly to the 
mantle tubercle. These papillae are very light brown in color. 
