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GEOLOGY OF THE FIRST DISTRICT. 
INFUSORIA. 
At the time the article on Alluvial Deposits was printed, the third part of Prof. Bailey’s 
Paper on American Bacillaria was not completed. It necessarily comes into the supplement, 
and is a part necessary to the description of the Infusoria of the First district of New-York. 
It is as follows :* 
The section Echinellea contains those Bacillaria which are fixed, that is, attached either by 
their extremities, or by a pedicel, to other bodies. They are all siliceous. 
The section Lacernata includes those which have a double covering. They consist of 
groups of siliceous individuals, surrounded by a common gelatinous mass, or enveloped by a 
membranous tube. 
As many species of each of these sections are often found spontaneously or accidentally 
separated from their pedicels or tubes, there is great chance of mistaking them for species of 
Naviculacea. 
Section III. ECHINELLEA. 
IsTHMiA. Fixed by one end; carapace or lorica siliceous, simple, broader than long, catenate by 
imperfect spontaneous division; individuals making various angles with each other, and con¬ 
nected by a narrow isthmus or neck-like process. 
Two species of this genus have been detected, viz. I. enervis, and 7. ohliquata. Neither 
of these have, to my knowledge, yet been detected in the United States; but as the latter is 
a pelagic species which has been found in places so different and distant from each other as 
Iceland, England, the Canary islands. Cape of Good Hope, &c., there can be little doubt 
that it will yet be found growing on some of our marine Algae. The first specimen which I 
ever saw, I detected on a dry specimen of Odonthalia dentata from Iceland. I have since 
received fine English specimens from E. J. Quekett, Esq. of London. Few microscopic 
objects exceed in beauty these little gems of the ocean. I have proved that their carapace is 
siliceous, by the proper chemical tests. A good idea of the general form of this genus may 
be got from Plate 4, fig. 153, of Pritchard’s Infusoria. 
SvNEDRA. Carapace simple, siliceous; fixed when young by one extremity, when older often free, 
longer than broad ; foot either wanting or rudimentary; form elongated or prismatic. 
Synedra -? (PL 42, fig. 1.) Frustules long, slender, linear, adhering laterally into plates which 
are supported by a short fleshy pedicel, and terminated by a fleshy mass. 
The species whose usual appearance is shown in PI. 42, fig. 1, occurs in vast quantities on 
various algae in the Hudson river at West-Point. It usually completely envelopes the plants 
to which it is attached, giving them a covering of bristling crystal-like particles, through 
Prof. Bailey’s Part 3 of American Bacillaria, from the American Journal of Science, Vol, 43, p. 3 to 13. 
