XLIV 



ON DYSTERIA; A NET/ GENUS OF INFUSORIA 

 Quart. Journ. Microsc. Sci., vol. v., 1857,//. 78-82 



The credit of the discovery of the animal which will be described 

 in the following pages is due to my friend Mr. Dyster, of Tenby ; and 

 many of the most important statements regarding its structure and 

 habits are based upon his observations. I think, therefore, I cannot 

 do better than name the genus of which it will form the type after him. ^ 



The creature was found in swarms among the algae coating the 

 shells of a Patella and of a Littorina which had long inhabited a 

 marine vivarium. I had the opportunity of examining its structure 

 when visiting my friend during the past autumn, and the following 

 paper must be regarded as an account of Mr. Dyster's work, with 

 some additions of my own. 



Dysteria arniata (PL VII. [XXX.] fig. 13), has an oval body, 

 TiToth — sTTrth of an inch long, by x^uth — xioth broad, which is not 

 altogether symmetrical — the one side presenting a considerable, evenly 

 rounded convexity, while the other, less prominent, is divided by an 

 angulated, longitudinal ridge {in, k) into a smaller, dorsal, and a larger, 

 ventral area. The edges of both lateral surfaces are sharp and thin ; 

 dorsally they are separated by a shallow groove {n, 0), but along the 

 ventral line of the body the groove is deep and narrow, and the pro- 

 duced edges of the lateral parietes (« 0) resemble the valves of a 

 bivalve shell. 



The ventral and dorsal grooves pass into one another in front,, 

 but posteriorly the lateral edges are united for a short space (/?). The 

 edge of the left, less convex, side of the body ends anteriorly in an 



' Sticklers for classical terminology may however, if they please, derive the name from 

 Sis and Tcpos, "a difficult sort of monster,'' or otherwise, from Suo-rtpis, "perversely 

 disputatious," on account of the controversies to which the obscure structure of the animal 

 may give rise. 



