290 Sketch of the Infusoria of the family Bacillaria. 
PENTASTERIAS. 
Free, a ast univalve pentagonal carapace. 
1. Pentasterias margaritifera. Surface granulated, rays thick and 
obtuse. Mandl. and Ehrenberg, |. ¢. Pl. 8, fig. 46. 
I am unacquainted with this genus, unless it is founded on five- 
rayed bodies resembling figure 7, which are only varieties of fig- 
ures 3 and 4; the number of arms being, as I have repeatedly 
seen, liable to much variation. 
'TESSARARTHRA. 
Free,. a simple carapace, univalve, g clobular,. smooth, forming 
chains. of four or more individ luals by spontaneous division. - 
1. Tessararthra moniliformis. aaa green, two or four uni- 
ted in a right line. M. and E. 1. c. Pl. 8, fig. 4 
-Lhave not noticed this genus in Arnerica, 
SPHERASTRUM. 
| ae a simple carapace, wnivalve smooth, inflated, forming 
groups of various forms by imperfect spontaneous division. 
I have not yet detected any specimens of this genus. 
X-ANTHIDIUM. 
| Free, carapace simple, univalve, globular, bristhng ui jis 
_ or sete, isolated, binary or quaternary, (catenate?) — 
This genus is very interesting, from the fact that bodisk, almost 
identical in form with the living species, occur abundantly, pre- 
served in the fossil state in flint. Drawings of several fossil spe- 
cies may be seen in the Annals of Natural History, Pl. 9, accom 
panying an interesting paper on the Organic Remains in the Flint 
of Chalk, by the Rev. J. B. Reade. The directions. given for 
finding thao bodies in flint, are “to chip off thin fragments 
which may be attached by means of Canada balsam to slips of 
‘glass, and then coated on the outer surface with hard spirit val 
nish. A hundred specimens may be thus cut, polished, and 
mounted for the microscope without trouble and expense, and in 
less time than an expert lapidary could prepare a single slice with 
the diamond mill and’ polishing tool” Many of the common 
gui flints coritain these bodies. Tam indebted to EK. J J. Quekett, 
‘Esq. of ‘London, for very fine specimens of fossil Xanthidia$ ; 
among them is a slice of flint prepared by a lapidary, which con 
tains in a space of less than a square inch, as many as eight or t¢? 
very perfect Xanthidia, saaestt tice oaes organic. bodies- 
