GENUS URCEOLARIA. 649 



trations, appears under moderate amplification to be continuous and 

 denticulate only on its outer edge ; the number of denticulations as figured 

 by these authorities corresponds with that of the form last described. 

 Hab. — Fresh water, on a species of Planarian. 



Trichodina digitodiscus, Stein. 



Animalcules similar in aspect to T. pedicuhis, but of smaller size, the 

 posterior adhesive disc, as seen under moderate magnification, apparently 

 containing two horny rings, the outer and more slender one being finely 

 denticulate on the outer margin only, and the smaller but thicker inner 

 one having from twelve to fourteen stout uncini on the outside, and also 

 numerous very fine, short, bristle-like denticulations on the interior margin. 



Hab. — Fresh water, on the brown polype Hydra vulgaris, more than 

 on H. viridis. 



Trichodina baltica, Quenn. Pl. XXXIII. Figs. 19-21. 



Body turban-shaped, the height when elevated nearly equalling the 

 diameter ; horny ring of the suctorial disc toothed on both its outer and 

 inner border, the outer teeth slender, uncinate, and recurved outwards, the 

 inner ones smaller, straight, and aculeate. Diameter of body 1-575" to 

 1-400". Hab. — Salt water, on Neritina fluviatilis. 



Apart from its marine habitat, this species may be distinguished from T. pedi- 

 cuhis by the character of the denticles of the chitinous ring that lines the posterior 

 acetabulum. These are of a considerably more slender character, and are united 

 with each other, as shown in the accompanying figure, reproduced from Quennerstedt,* 

 on an apparently entirely distinct system. 



Trichodina scorpaena, Robin. Pl. XXXI. Figs. 46 and 47. 



Body turban-shaped, the superior surface convex, dome-like, the inferior 

 one concave ; cilia of circular peristomal wreath larger than those of the 

 posterior border ; horny armature of acetabulum apparently resembling 

 that of Trichodina pediculus. Diameter of body 1-600". 



Hab. — Salt water, on the branchia of fish belonging to the genera 

 Scoi'pmia and Trigla. 



This species is figured and briefly described by Professor Ch. Robin in the 

 'Journal de I'Anatomie et Physiologic,' tom. xv., 1879. See also 'Journal of the 

 Royal Microscopical Society,' London, October 1880. 



Genus H. URCEOLARIA, Stein. 



Animalcules similar to those of Trichodina, but the adherent sucking- 

 disc or acetabulum provided with a simply striated, non-denticulate 

 corneous ring ; the anterior region usually more attenuate, and with the 

 peristome obliquely set. 



* ' Sveriges Infusoriefauna,' Heft iii., 1869. 



