A. E. Verrill—Mollusca of the New England Coast. — 20% 
slight, rounded, median notch; the surface is marked with faint 
radiating grooves, and is uniformly covered with small rounded 
granules. The succeeding valves have their posterior border nearly 
straight, with a slightly projecting, obtuse, median beak, from which 
run well-marked, elevated, rounded diagonal ribs; the lateral areas 
are somewhat raised, with a depression next the ribs, and their sur- 
face is covered with small, low rounded granules, more distinct than 
those on the median areas, which appear nearly smooth to the naked 
eye, but are crossed by evident transverse lines of growth. The 
posterior valye has the posterior edge a little upturned, and slightly 
emarginate in the middle, with a submarginal, raised rib near the 
posterior margin above; the upper edge overhangs the lower 
lamina but slightly, or not at all, in the smaller specimens, with a 
deep groove between; the lower lamina is more deeply emarginate, 
in the middle, than the upper one, with wider laminz each side of 
the notch, but in the lacgest example the upper portion is divided 
into several laning, and projects decidedly beyond the lower, while 
the notch is obsolete. (Perhaps this is due to injury during life.) 
When detached. the insevved edges of the valves are very narrow, 
the front edge of the anterior valve is narrower <han the upper, 
lamina thickened and diviced into numerous (about thirty) small, 
rough and vnequal denticles, which become obsolete near the lateral 
angles. The median plates have the lateral insertion plates small, 
treneate, not projecung beyond the upper lamina, with a well- 
marked groove between, and separated from the anterior insertion 
plates by a deep narrow notch, in line with the diagonal ribs; the 
anterior plates are broadly rounded, not very wide, separated by a 
raiber wide rounded median notch. 
Color of marginal membrane dull rusty or yellowish brown; shell 
grayish white, stained with brown. 
Length of the largest specimen, in alcohol, 32™™; its greatest 
breadth, 26™™; length of shell, 21™"; greatest breadth, 18""; length 
of anterior valve, 4"; its breadth, 15°5"™; length of exposed part 
of 3d valve, 4™™; of posterior valve, 4°7™™; its breadth, 8"™; ex- 
tent of marginal membrane beyond the shell, anteriorly, 12™™; 
length of foot, 12™"; breadth of foot, 8™"; length of head, 3™™; 
breadth, 7™™. 
A small specimen is 21" long; breadth, 16™"; expanse of mem- 
brane in front of shell, 6°5™"; length of shell, 16™™ ; its breadth, 13°5™™. 
When living the marginal membrane was relatively broader. 
