GENUS PRORODON. 491 



lateral border of the ventral surface ; cuticular surface delicately striate 

 longitudinally, cilia closely set, long, fine, and matted ; the anterior ex- 

 tremity apparently bearing a small fascicle of longer setose cilia ; contrac- 

 tile vesicle spherical, subcentral, exhibiting at diastole minute, supple- 

 mentary peripheral lacunae ; endoplast consisting of as many as seven 

 nucleus-like corpuscles, disposed in a row parallel with the posterior and 

 right-lateral border. Length 186" to 1-270". 



HAB. Body-slime of Succinea amphibia, and also that of many land 

 snails, including Helix hortensis. 



The more anterior location of the oral fossa, together with the animalcule's 

 separate habitat, serves to distinguish this form from the two accompanying repre- 

 sentatives of the genus. 



Conchophthirus curtus, Eng. 



Body shortly oval, nearly as broad as long, equally rounded at both 

 extremities, the dorsal surface highly convex, the ventral one flattened ; 

 oral fossa subcentral, very small, continued into a long, recurved, tubular 

 pharynx ; cuticular surface delicately striate longitudinally, clothed through- 

 out with long, fine, matted cilia ; endoplast oval, subcentral, contractile 

 vesicle located a little behind this structure, stelliform or rosette-shaped at 

 the time of diastole. Length 1-200." 



HAB. Mucilage of the fresh-water mussel Unio crassus, in company 

 with C. anodontce. 



Although found in company with Conchophthirus anodonta, Engelmann considers 

 that the shorter or more orbicular, contour of the body, together with the smaller 

 comparative size of the oral fossa, distinguishes it sufficiently for separate specific 

 recognition ; the character of the contractile vesicle affords another point of 

 differentiation. 



Fam. II. PRORODONTID-ffi, S.K. 



Animalcules free-swimming, symmetrically ovate or cylindrical, entirely 

 ciliate ; oral and cuticular cilia alike in size and character ; oral aperture 

 terminal or lateral ; pharynx distinct, usually plicate or armed with rod-like 

 teeth. 



This family group coincides most nearly with the Decteria of Max Perty (vol. i. 

 p. 204), which is restricted exclusively, however, to those genera in which the 

 pharynx is armed with rod-like teeth. By Stein, the very closely allied genera Proro- 

 don and Nassula are, as shown in his classificatory system, reproduced at page 210 

 of vol. i., distributed among his two very heterogeneous families of the Enchelina 

 and Paramaecina. 



GENUS I. PRORODON, Ehrenberg. 



Animalcules persistent in shape, symmetrically ovate, cylindrical or 

 slightly compressed, rounded at the extremities, entirely and evenly ciliate 

 throughout; the oral orifice situated at or closely adjacent to the anterior pole, 

 and the anal aperture at the opposite or posterior one; pharynx strengthened 

 by a special induration consisting usually of rod-like teeth, but sometimes 



C 2 



