Descriptions of some Shells, &c. 347 
other, viz. 1. The increased pressure on the anterior disc of the 
moving body, arising from its motion. 2. The diminished pressure 
on the posterior disc. 3. The friction of the fluid on the surface of 
the body.—By the application of a novel and curious process of 
analysis, he has most ingeniously contrived to separate this resist- 
ance into these three constituent elements, and to examine the value 
and efficiency of each in numerous and distinct classes of experi- 
ments. This mode of viewing and treating the subject will at once 
commend itself to every one who has given his attention to this de- 
partment of hydraulics. 
These experiments of Beaufoy have developed a vast number of 
facts which are of great value in themselves considered,—yet this 
value is scarcely appreciable, when compared with that which they 
possess as indices pointing to those general principles, the develop- 
ment of which was the ultimate object of all his labors. With ref- 
erence to this object he has collated and classified his experiments 
with great care and judgment, and doubtless they will eventually 
become the basis on which will be erected a theoretical superstruc- 
ture worthy of so magnificent a foundation. 
I look with great interest for the ‘“'Tentamen Theorie Resisten- 
tie Fluidorum Constituenda” of Assessor Lagerhjelm, promised in 
a future volume. 
Very respectfully yours, 
Eur W. Brake. 
New Haven, Conn., June, 1835. 
Arr. XXVII.— Descriptions of some Shells, belonging to the Coast 
of New England; by Jos. G. Vorren. No. 2. 
Genus Anatina, Lam. 
A. papyratia? Say. Plate, Fig. 1, a, 6, ¢, d. 
Shell, subovate, moderately convex, thin, fragile, valves nearly 
equal, gaping, not widely, at the posterior margin: beaks, not prom- 
inent, placed at about one third the length of the shell from the pos- 
terior end: surface, finely wrinkled concentrically, white, somewhat 
pearly, covered with a yellowish-white epidermis : dorsal margin, 
straight, behind the beaks: posterior margin, also straight, forming 
obtuse angles with the dorsal and posterior-basal margins; a slight 
Wave, extending from the beaks to the lower angle, forms an indis- 
