78 HUXLEY, ON DYSTERIA. 



On Dysteria ; a new genus of Infusoria. 

 By Thomas H. Huxley, F.R.S. 



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 state- 

 ments 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 ex- 

 amining 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 armata (PI. VII, fig. 13,) has an oval body, 

 ^Joth — o^dth of an inch long, by 4 J^th — j^o^^^ 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 [m, 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,o), but along the ventral 

 line of the body the groove is deep and narrow, and the 

 produced edges of the lateral parietes {n, 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 {h) . The edge of the left, less convex, side of the body 

 ends anteriorly in an obtuse point [m), which corresponds 

 with the anterior termination of the angulated ridge, and 

 does not extend, by any means so far forward, as the edge of 

 the right side, which remains thin, and forms the anterior 

 extremity of the body. 



At the anterior extremity the large oral apertm'e («) is seen, 

 just below the angulated ridge and occupying the bottom of 

 a deep fossa, which here takes the place of the dorsal and 

 ventral grooves. The left wall of this fossa is thickened, and 

 projects inwards so as to form a cushion-like lobe, clothed 



* Sticklers for classical tcrminolofry may however, if they please, derive 

 the name from Svc, and npoQ, " a difficult sort of monster," or otherwise, 

 from SuartpiQ, ' perversely disputations," on account of the controversies to 

 which the obscure structure of the animal may give rise. 



