Improved Air Pump Receiver. 353 
This is undoubtedly the same shell that was described by me in 
this Journal, Vol. xxvi, p. 369, and named Pasithea nigra. I had 
then before me several hundred individuals, all living, from the 
length of 0.15 of an inch down to less than 0.10 of an inch, and 
did not suspect that all were immature. I was, however, much 
puzzled by its characters, and could find no place for it elsewhere, 
than in Mr. Lea’s new genus Pastthea. I am now indebted to Dr. 
A. A. Gould of Boston, (through the kind agency of the Rev. F. 
W. P. Greenwood) for the means of making this correction, as well 
as for the intimation that I had been occupied with the young, only, 
of the species. The change in the form of the aperture of this 
‘Shell, with increasing maturity, is interesting. While quite young, 
it might be considered a Turbo; and Dr. Gould states that it was 
regarded, by some, as the Turbo calathiscus of Montague, and so 
catalogued: Mr. Greenwood suggests that it may be Say’s Turri- 
tella alternata, and the half-grown specimens agree pretty well with 
Say’s description of that species; and in the state in which I de- 
scribed it, the future well marked beak and canal] are indicated only 
by a scarcely perceptible arcuation at the base. The shell descri- 
bed by Say in “ American Conchology, No. 5,” as C. ferrugineum 
bears a resemblance to this; but his description does not accord 
with some marks which appear to be constant in our shell. I take 
pleasure in affixing the name suggested by Dr. Gould. 
Arr. XXVIII.—Improved Air Pump Receiver, exhibited before 
the New York Mechanic’s Institute, Jan. 1835 ; by Joun Bett, 
Member of the Institute. 
TO PROFESSOR SILLIMAN. 
Dear Sir,—I send you herewith the drawings and description of 
an apparatus for creating a more perfect vacuum, than can usually 
be obtained by the common or silk-valve air pump. It is the inven- 
tion of Mr. John Bell of this city, and is the subject of a paper by 
that gentleman recently read before the Mechanic’s Institute of the 
city of New York, by which body I am requested to forward to you 
the description and drawing of the apparatus, that if you deem them 
worthy, they may find a place in your valuable Journal. 
Yours, &c. L. D. Gate, 
Cor. Sec. Mechanic’s Institute of the City of New York. 
Vor. XXVIIL.—No. 2. 
