186 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
golden white and glistening and are marked with white spots. 
On the lower surface of the branchial syphon are numerous short, 
truncate papillae. The end of the anal syphon is encircled with 
similar papillae to those encircling the branchial syphon. The 
valve is large and prominent, mottled with white spots. In 
Fig. 39. — Solen ensis Linn6. 
the young, 1.5 milHmeters in length, the shell is much broader 
compared to its length than in the adult (Fig. 39, h). The 
protoconch is orbicular and the next stage as outhned in the 
figure resembles closely a similar stage in Machaera costata. The 
syphons at this stage are very short and sustain a few slender 
papillae with wide spaces between (Fig. 39, c). 
MACHAERA COSTATA Gould. 
Fig. 40. Length, 44 mm. 
This is one of our most beautiful shells. The foot is large 
and presents, when expanded, a truncate form in front; it may 
extend to nearly the length of the shell. The mantle extends 
beyond the entire margin of the shell even to the beaks anteriorly. 
The syphons and mantle are densely clothed with papUlae, those 
on the syphons very short and simple ; at the base of the syphons 
they begin to grow larger, and along the ventral portion of the 
mantle become longer and fimbriated, almost arborescent, with 
minute papillae at their base and even on the face of the larger 
