GENUS D YSTERIA. 753 



of Dysteria was altogether too complex for an infusorial animalcule, and that its 

 correct position was more probably among the more highly organized Rotifera some- 

 where near the genera Monocerca and Mastigocerca. Mr. Gosse at the same time sug- 

 gested that this type might be regarded as an annectant form between the Rotiferae 

 and the Ciliate Infusoria. Among the large number of undoubted Infusoria now known 

 to possess an essentially equivalent type of structure, and here included under the 

 family title of the Dysteriidae, those assembled under the new generic title of Cypridium 

 most closely resemble the present type. These in a like manner possess a somewhat 

 unsymmetrical bivalvular carapace, the dorsal borders of which are posteriorly 

 united to one another, and are also provided with a similar posteriorly attached 

 caudal style. The only substantial point of distinction between the two is found 

 in the character of the pharyngeal armature, which in Dysteria is far more complex 

 than in other members of the same family group. 



The more minute details of the indurated pharyngeal apparatus of Dysteria, 

 as described by Professor Huxley, may be suitably reproduced. The oral fossa 

 is, in the first instance, strengthened by a curious curved rod, which terminates 

 superiorly in a bifid tooth, while inferiorly it appears to become lost in the walls 

 of the fossa. This is followed by the pharyngeal apparatus proper, which may 

 be said to consist of two portions an anterior, somewhat rounded mass, in appo- 

 sition with a much elongated, styliform posterior portion. As intimated by Prof. 

 Huxley, it is very difficult to assure oneself of the precise structure of the complex 

 anterior portion. It appears, however, to form a deep ring composed of three 

 pieces two supero-lateral and mutually corresponding, united with a third, inferior, 

 azygos portion. The element last named is somewhat triangular, with a broad 

 base and rounded obtuse apex. This apex is directed forwards and immediately 

 underlies the oral aperture, while the base is turned backwards and unites with 

 the two supero-lateral pieces. Each of these latter is concave internally, and convex 

 externally, so as to form a segment of a circle, and presents a clear median space, 

 the optical expression either of a perforation or of a much-thinned spot. The 

 anterior edge of each supero-lateral piece is nearly straight, but the posterior border is 

 convex, and articulates with, or is apposed to, the anterior extremity of the posterior 

 or styliform division of the apparatus. Viewed laterally, this posterior portion 

 appears to consist of two styles which are somewhat like nails in shape, their 

 anterior extremities being truncated so as to somewhat resemble a nail-head, 

 while the posterior extremity seems to taper to a fine point. Rather in front of the 

 middle of its inferior edge each style apparently gives off a short process downwards, 

 which process is, in botanical language, decurrent upon the style. Careful examina- 

 tion of the dorsal or ventral aspect of these parts shows that the decurrent process is 

 in fact only the optical expression of a delicate membrane, which is bent so as to 

 have a ventral convexity, and connects together the two styles. It might be said, 

 therefore, that the posterior part of the apparatus is a triangular membrane, deeply 

 excavated in front, bent so as to be convex downwards, and having its margins 

 thickened and produced into styliform enlargements. This curious piece of 

 mechanism is directed upwards and backwards, and terminates in the substance of 

 the body without any apparent connection with other parts. 



From the foregoing description of the pharyngeal armature of Dysteria as recorded 

 by Professor Huxley, it is evident that the elongate and backward produced so-called 

 styliform appendage or posterior portion only of this apparatus coincides with the 

 more ordinary pharyngeal armature of Iduna, <dEgyria, and other representatives of 

 the same and preceding family groups, the components of the complex annular 

 anterior portion being entirely accessory. It may be further remarked that this 

 coincident pharyngeal portion, as above described, exhibits a type of structure midway 

 between that of the simply tubular corneous induration of Iduna and the cylindrical 

 rod-fascicle of such types as Chlamydodon and Chilodon, The animalcules which fur- 

 nished the material for Professor Huxley's description were remitted him by 

 Mr. Dyster, in whose honour the genus was named, and were found in swarms 

 among confervoid algae that coated the shells of a Patella and a Littorina which had 



VOL. II. U 



