752 ORDER HYPOTRICHA. 



has been greatly augmented by the researches of Messrs. ClaparMe and Lachmann* 

 recorded in their well-known 'Etudes sur les Infusoires,' pubhshed in the years 

 1858-60. 



Genus I. IDUNA, C. & L. 



Animalcules free-swimming, encuirassed, oblong, bilaterally compressed ; 

 carapace formed of two distinct, entirely separate plates or valves, one 

 being developed on each side of the body ; a tail-like style or spine pro- 

 jecting from the posterior extremity of the narrow and finely ciliated ventral 

 groove ; the oral aperture opening on the antero-ventral border ; pharyngeal 

 armature consisting of a single subcylindrical horny tube. 



Iduna sulcata, C. & L. Pl. XLII. Figs. 24-26. 



Right valve of the carapace convex, raised into four longitudinal, elevated, 

 angular costae ; the left valve plane, perfectly smooth, not descending so 

 low on the ventral border as the opposite one ; tail-like style short and 

 conical ; contractile vesicles two in number ; pharyngeal tube bent. Length 

 of body 1-175". Hab. — Salt water : Norwegian coast (C. & L.). 



Genus II. DYSTERIA, Huxley. 



Animalcules free-swimming, ovoid, encuirassed, bilaterally compressed ; 

 the ventral surface entirely ciliate, narrow, and groove-like ; carapace com- 

 posed of two lateral pieces, united to each at the posterior end only of the 

 dorsal margin ; pharyngeal armature complex, consisting of an annular, 

 compound, anterior, horny portion, and a long, posteriorly produced stylate 

 process ; a tail-like spine projecting from the posterior region of the ventral 

 groove. 



Dysteria armata, Hux. Pl. XLII. Figs. 27-30. 



Valves of carapace oval, the right one more convex, its surface smooth ; 

 the left valve traversed near its dorsal margin by a longitudinal angular 

 ridcre, not extending so far forward as the right one ; ventral style lanceo- 

 late, situated at a distance of one-fifth of the length of the body from the 

 posterior extremity, its proximal portion hollow; stylate process of the 

 pharynx produced upwards and backwards through the centre of the body 

 to the point opposite the origin of the ventral style ; the contractile vesicle 

 single, subcentral ; an amethyst-coloured globule or pigment-spot invariably 

 developed immediately above the anterior or annular portion of the pharynx. 

 Length of body 1-350" to 1-250". Hab.— Salt water. 



Immediately succeeding the description of this animalcule by Professor Huxley * 

 some discussion arose concerning the question of its true affinities. While its 

 discoverer pointed out, what is now a generally acknowledged fact, that it exhibited 

 a close structural correspondence with the Euplotcs {.^gyria) monostyla, misquoted 

 " macrostjla" and the Chlamydodon vuiemosyne of Ehrenberg, Mr. P. H. Gosse, 

 dissenting from this interpretation, advocated the opinion f that the structure 



* 'Journal of Microscopical Science,' 1857, p. 78. f Ibid., p. 138. 



