290 Sketch of the Infusoria of the family Badllaria. 



Pentasterias. 



Free, a simple univalve pentagonal carapace. 



1. Pentasterias margaritifera. Surface granulated, rays thick and 

 obtuse. Mandl. and Ehrenberg, 1. c. PI. 8, fig. 46. 



I am unacquainted with this genus, unless it is founded on five- 

 rayed bodies resembhng 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, globular, smooth, forming 

 chains of four or more individuals by spontatieous division. 



1. Tessararthra moniliformis. Corpuscles green, two or four uni- 

 ted in a right line. M. and E. 1. c. PL 8, fig. 47. 



I have not noticed this genus in America. 



Spherastrum. 



Free, a simple carapace, univalve smooth, inflated, forming 

 groups of various forms by imperfect spontaneous division. 

 I have not yet detected any specimens of this genus. 



Xanthidium. 



Free, carapace simple, univalve, globular, binstling with points 

 or setoi, isolated, binary or quaternary, [catenate ?) 



This genus is very interesting, from the fact that bodies, almost 

 identical in form with the living species, occur abundantly, pre- 

 served in the fossil state m flint. Drawings of several fossil spe- 

 cies may be seen in the Annals of Natural History, PI. 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 these 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 var- 

 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 

 gun flints contain these bodies. I am indebted to E. J. Cluekett, 

 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 ten 

 very perfect Xanthidia, a scale of a fish, and other organic bodies. 



