146 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
of expanding into a broad, pectinated disk which is thrust forward 
and then, suddenly contracting, propels itself in a series of vigor- 
ous leaps. Its nearest relatives Yoldia and Leda have the same 
methods of locomotion. Instead of a branchial and an anal 
syphon there is simply an opening behind, larger above, surrounded 
by papillae. The anal opening has on its sides a slightly longer 
prolongation of the mantle and supports a few papillae varying 
in size, one very much larger and digitated, and above, a large, 
single azygous tentacle. The demarcation between the two 
regions branchial and anal, is clearly defined by the form and 
arrangement of the papillae, as shown in the figure. The highly 
polished periosteum extends far beyond the margin of the shell; 
its surface repels water as if oiled and Professor Oilman A. Drew 
informs me that in digging them from the mud many of them 
floated on the surface of the water. For further details regarding 
the structure the student is referred to the memoir already 
mentioned. 
SOLEMYA BOREALIS Totten. 
Fig. 2. Length, 53 mm. 
The figure here given is copied from my memoir. While 
Solemya velum may be thrown up on our beaches after storms by 
the thousands, the larger species, *S. horealis, is of rare occurrence. 
Fig. 2. — Solemya horealis Totten. 
Fragments of the shell with its nearly black periosteum may now 
and then be found but of great rarity is a complete specimen. 
The creature lives in eight or ten fathoms, deeply buried in the 
mud, so that an ordinary dredge would never reach it. The 
