GENUS CALCEOLUS. 619 



Calceolus cypripedium, J.-Clark sp. PL. XXXII. FIGS. 23 AND 24. 



Body obliquely pyriform, widest anteriorly, hollowed on the ventral side 

 by a broad longitudinal depression, which commencing at a little distance 

 from the larger and rounded anterior end extends in a straight line to the 

 more attenuate posterior extremity ; encircled by two annular furrows, the 

 anterior and narrower one bearing a wreath of long powerful locomotive 

 cirri, the whole body from this point backwards clothed with finer vibratile 

 cilia, these more crowded and conspicuous on the posterior furrow, the 

 ventral surface of which is perforated by the oral aperture. A fascicle of 

 closely approximated setose cilia, presenting in their agglomerate condition 

 the aspect of a single flexible caudal appendage, originating from the 

 posterior furrow at a little distance behind the mouth, and projecting 

 beyond the posterior extremity to an extent equal in length to that of one- 

 third of the whole body. Contractile vesicle large, spherical in diastole, 

 situated centrally close to the posterior extremity ; endoplast band-like, 

 curved, located immediately above the contractile vesicle, its two extre- 

 mities descending and embracing that structure on each side. Length of 

 body 1-300" to 1-150". HAB. Fresh water. Colour, light brown. 



Although introduced by H. James-Clark* as a representative of the genus 

 Peridinium, there can be little or no doubt, as first pointed out by Stein, that the true 

 place of this species is much nearer to that of Urocentrum turbo. In general contour 

 and in habits it in fact corresponds so closely with this type as to be apparently 

 referable to the same generic group. The one distinctive character, however, 

 afforded by the complete ciliation, with the exception of the anterior skull-cap- 

 shaped border, of the general cuticular surface, necessitates its isolation from the 

 typical smooth-bodied Peritricha. While thus separated, it may at the same time be 

 said to represent one of the most conspicuous annectant forms between the two orders 

 of the Heterotricha and Peritricha, and to exhibit the same relationship with reference 

 to the genus Urocentrum as is held by Trichodinopsis and Strombidinopsis respectively 

 with regard to the genera Trichodina and Strombidium. The movements of this 

 animalcule in the water accord entirely with those of Urocentrum turbo, consisting 

 chiefly of a vigorous rotatory motion to and fro on its long axis, it being often 

 temporarily attached under such circumstances to some solid substance by the 

 extremity of its adhesive caudal appendage, and upon which it revolves as though 

 on a pivot. This sedentary condition is in like manner frequently changed for a 

 more active natatory one, and in which it darts in a straight line from one place to 

 another with amazing swiftness, tacking, as it were, now and then to one side or 

 the other, and apparently utilizing its posterior caudal fascicle after the manner of a 

 rudder. Multiplication by transverse fission is the only reproductive phenomenon 

 that has so far been observed with reference to this type. The contractile vesicle 

 was observed by Professor Clark to assume a somewhat irregular outline between 

 diastole and systole, but does not appear to possess distinct lateral sinuses as has 

 been observed by the present author of Urocentrum turbo. 



* ' Proceedings of the American Academy of Science,' February 1865. 



