304 Sketch of the Infusoria of the family Bacillaria. 



entering fold of the carapace, Hab. ponds near West Point. A 

 similar fold in the carapace is visible in some species of Euastrum. 

 (See fig. 27, PL 1.) 



MiCROTHECA. 



jPree, carapace simple, univalve, compressed, separate, lamelli- 

 form. 



M. octoceros. Carapace quadrangular, hyaline, four spines at each 

 end, internal body golden yellow. 



I am unacquainted with this genus. 



End of the Desmidiacea. 



Note. — Having, in what precedes, completed a sketch of the Desmi- 

 diacea, I propose to offer in the next part of this memoir (now nearly 

 ready for the press) some account of the other divisions of the Bacilla- 

 ria, viz. the Naviadacea, the Echinellea and the Lacernata. Many of 

 the species of these families have siliceous coverings and are found in 

 a, fossil state. An account of our American species will therefore, I 

 trust, be found of some interest to American geologists, especially as 

 the recent discovery by Prof W. B. Rogers, of the vast infusorial stra- 

 tum in the tertiary of Virginia,* cannot fail to attract new attention to 

 these interesting bodies. 



Explanation of the Figures, on Plate I. — The sketches which accom- 

 pany this memoir, were all made by means of a camera lucida eye- 

 piece attached to Chevalier's horizontal and vertical microscope. Li 

 fig. 39 is shown a sketch of ^^tyV^^s of a millimetre, magnified and drawn 

 with the same combination of lenses, camera lucida, distance, &c. This 

 being equally magnified with the drawings, will serve as a scale to de- 

 termine the absolute dimensions of any of the objects. The highest 

 power of the instrument was not used in getting the outlines, as it would 

 have given figures inconveniently large. The details were, however, 

 occasionally corrected or confirmed, by the use of a higher power. 



PLATE I. 



Fig. 1. Desmidium Schwartzii, page 288, from a twisted portion of a 

 filament. 



Fig. 2 and 3. Euastrum ? page 296, two positions of same individual. 



Fig. 4 and 5. Euastrum ? a larger variety of the same species as fig. 3. 



Fig. 5. Shows the same in side view, the lower half being in a state 

 of imperfect development. 



Fig. 6. Variety of fig. 3 ? 



Fig. 7. Five-armed variety of fig. 4, page 296. 



* ^^^ -^^Qfi^ce of this discovery in the present volume of this Journal, p. 214. 



