ACEPHALA. 9 
N. pe.puinoponta, Migh. et Ad., Bost. Jour. iv. 40. 
Stimpson, Bost. Proc. iv. 13.— Lamin. Whole 
Coast. 
Lepa THrRact£Formis, Stimpson, Bost. Proc. iv. 26. 
Nucula thracieformis, Storer. Gould, 97, f.66. NV. na- 
_ vicularis, Couth. Gould, 103.— Corall. St. Andrew’s 
“Bay in 10 f. and off Head Harbor, Campo-bello, in 
40 f.(W.S8.) In deep water off the coasts of Maine 
and Massachusetts, and off Race Pt., Cape Cod, in 
30 f. Off Fire Island, L. L, in 10 £(C. S,) 
The genus Leda was separated from Nucula by 
Schumacher in 1817. It presents great differences 
from that genus as now restricted, both in animal and 
shell; — Nucula having its mantle open through- 
out, without siphons, while in Leda they are well 
developed. (See Moller, Index Moll. Grénl.; Lovén, 
Index Moll. Scand. 34; and Forbes and Hanley, Brit. 
Moll., ii. 214.) Under Moller’s genus Yoldia —“ Ani- 
mal tubis longis curvatis instructum; pede magno, va- 
lido ; pallio toto aperto, marginibus posticé ciliatis ” — 
will come our species thracieformis, obesa, sapotilla, 
Cascoensis, myalis, and limatula, the animals of nearly 
all of which I have examined. In some of them the 
mantle is ciliated all around, and it has two thick- 
enings, one anteriorly just before the foot, and 
one posteriorly just before the siphons. In ZL. lima- 
tula I have seen the produced exterior palpi protrud- 
ed from the posterior thickened margins, as from a 
sheath, — the palpi gyrating rapidly in the water as if 
in search of food. L. tenwisulcata has no such struct- 
2 
