634 ORDER PERITRICHA. 



The discoverers of this species record that its motions in the water are remark- 

 ably swift and difficult to follow, as also that specimens occasionally in the midst of 

 their impetuous course suddenly fall to pieces, as though by magic, undergoing 

 diffluence with a rapidity observed of no other animalcule, though to some extent 

 approached in Arachnidhun globosus. According to the recent investigations of 

 Biitschli,* the cuticular layer in this species is armed midway between the centre of 

 the body and the anterior margin with an even girdle of elongate, close-set 

 trichocysts. The figure accompanying the account of this variety seems, however, 

 to represent a distinct species, possessing a more elongate contour, and exhibiting 

 no trace of the posterior furrows that characterize Claparede and Lachmann's type. 

 It is here proposed to provisionally distinguish this last-named animalcule by the 

 title of Strombidmm Biltschlii. 



Strombidium turbo, C. & L, 



Body globose, slightly conical posteriorly, its surface smooth ; adoral 

 cirri equalling the body in length, very rigid. Length 1-700". 

 Hab. — Fresh water. 



Strombidium Claparedi, S. K. Pl. XXXII. Fig. 46. 



Body smooth, transparent, elongate-pyriform, tapering posteriorly, about 

 twice as long as broad. Length 1-300". 

 Hab. — Pond water, among Conferva. 



This, the largest recorded species of the genus, is easily recognized by its elongate 

 outline, and seems to be identical with a fresh-water species imperfectly observed by 

 Claparede and Lachmann,"]" but for which they have not proposed a distinct specific 

 title. Its movements agree with those recorded in the above generic description, 

 and correspond remarkably with those of Urocentnun turbo. On several occasions 

 this species has been observed by the author to attach itself to aquatic plants, or 

 other objects, by its posterior extremity, which appears to be of softer consistence 

 than the remainder of the body, and thus fixed draws currents of food-laden water 

 towards it by the vigorous vibratory action of its powerful adoral cilia, after the 

 manner of a Vorticella. Such a sedentary condition was only temporarily maintained, 

 the animalcule soon resuming its more active gyratoiy course. 



Strombidium urceolare, Stein. 



Body contracted centrally, anteriorly moderately, and posteriorly con- 

 siderably enlarged, almost pitcher-shaped ; peristome produced towards 

 the posterior extremity as an oblique furrow, bearing towards its anterior 

 extremity two or three closely set, large-sized vibratile cilia ; endoplast 

 small, oval ; contractile vesicle posteriorly situated. Dimensions unre- 

 corded. Hab. — Salt water : Baltic Sea. 



Strombidium acuminatum, Stein. 



Body attenuate, conical, acuminate anteriorly ; peristome produced 

 backwards nearly to the centre of the body ; the hinder half of the ventral 

 surface bearing an oblique supplementary row of fine vibratile cilia ; 

 colour yellow. Dimensions unrecorded. 



Hab. — Salt water : Baltic Sea. 



* ' Archiv fiir Mikroskopischer Anatomic,' Bd. ix., 1873. f ' Etudes sur les Infusoires,' p. 372. 



