152 SKETCH OF TIIR INI'USORIA 



2. FragUlaria trionodis. Ehrcnberg mentions this species as oc- 

 curring in a fossil stateat West Toint. I am ignorant of its charac- 

 ters, and may have confounded it with F. j)ectmalh, to which species 

 nil the varieties occurring at West Point appear referable. 



MERIDION. 



Frec^ carapace simple, bivalve or multivalve {siliceous) pris- 

 matic, wed^eform, forming' fragile spiral chains which often ap- 

 pear like complete circles, and ivhich result from imperfect spon- 

 taneous division. 



Meridian vernale. (Tl. II, fig. 42, a, b.) Corpuscles wedgeform, 

 striate, anterior end truncate and dentate, polypidom spiral, often 

 appearing perfectly circular, ^V ^o ?V of ^ lii^e. M. circidare, Agardh. 

 M. circulare, Eutzing, Linn. 1833, PI. 15, fig. 37. 



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

 and excites gi-eat 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 millions and millions of these 

 exqviisitely 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 endochromc 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 fu-e and nitric acid. 



