104 Sketch of the Infusoria of the family Bacillaria. 



This is one of the most beautiful of the fresh-water infusoria, 

 and excites great admiration in all who behold its elegant form 

 and markings, under a good microscope. It occurs in immense 

 quantities in the mountain brooks around West Point, the bot- 

 toms of which are literally covered in the first warm days of 

 spring, with a ferruginous colored mucous matter, about one 

 quarter of an inch thick, which, on examination by the micro- 

 scope, proves to be filled with miUions and millions of these 

 exquisitely beautiful siliceous bodies. Every submerged stone, 

 twig, and spear of grass, is enveloped by them, and the waving 

 plume-like appearance of a filamentous body covered in this way, 

 is often very elegant. 



The spiral or helicoidal form of the chains is not easily per- 

 ceived, unless the chains are thrown on edge, (as in fig. 42, b.) 

 This is easily effected with Chevalier's compressor. 



Alcohol completely dissolves the endochrome of this species, 

 and the solution when evaporated, leaves a greenish resinous 

 mass. The frustules, after the action of alcohol, are as colorless 

 as glass, and resist the action of fire and nitric acid. 



End of the Naviculacecc. 



Explanation of the figures of Piate 2.— The figures which accom- 

 pany this memoir, were all drawn by the aid of a camera lucida, and 

 to the same scale as was used in the plates of the first part of this 

 sketch. That scale is shown in fig. 15, which represents yiy°yths of a 

 millimetre, magnified equally with the drawings. In the sketches, a 

 represents the side of the animal usually seen, Z», the other side. 



Fig. 1. Pyxidicula operculata, fossil from Manchester, Mass. — flu- 

 viatile. 



Fig. 1. a. Pyxidicula operculata .? fossil from Massachusetts. 



Fig. 2. a, h. Pyxidicula .? Fossil in infusorial stratum at Richmond, 

 Virginia. 



Fig. 3. Gaillonella moniliformis, recent, marine. 



Fig. 4. 4 a. Gaillonella aurichalcea, recent, fluviatile, at c is seen a 

 globular joint. 



Fig. 4. h. Gaillonella aurichalcea } recent, fluviatile. 



Fig. 5. Gaillonella distans, recent and fossil, fluviatile. 



Fig. 6. «, h. Gaillonella varians, recent and fossil, fluviatile. 



Fig. 7. «, 1). Gaillonella sulcata. Fossil at Richmond, Va., recent, 

 marine at Stonington, Conn. «, jointed cylinder composed of several 

 individuals ; h, base of one of the joints. 



Fig. 8. Gaillonella ? . Recent, brackish water of Hudson River 



at West Point. 



