294 ON A NEW PEEITBICHOUS INruSOttlAN. 



longed ; endoplast ribbou-like, placed longitudinally ; contractile 

 vesicle spherical, giving off a canal-like ramification, occasionally 

 brandling a second time, and extending to within a short dis- 

 tance of the ciliary disk." 



The second species, Gerda fixa, was discovered by D'Udekem 

 in a pond in the neighbourhood of Brussels, and described in 

 1864 ("Infusoires de la Belgique," Mem. Acad, Royale de la Bel- 

 gique, torn, xxxiv.). It is distinguished from the foregoing in 

 having a body of greater proportional length, the surface being 

 smooth, the body tapering abruptly, and terminating in a blunt 

 point ; the contractile vesicle is spherical and is situated close to 

 the vestibulum. 



In the new species about to be described, the body is elongated, 

 about seven times as long as broad, of an undulating contour, 

 subject to changes ; it is highly contractile, assuming a globular 

 shape when retracted ; the integument is of a reddish tint, and 

 transversely striate, annulate when contracted. The posterior 

 extremity of the body terminates in a peculiar imbricated tail- 

 like appendage, resembling the telescopic tail of a rotifer, but 

 is not telescopic ; this appendage is finely striate longitudinally ; 

 the body when extended, before the ciliary disk is projected, is 

 broad and rounded at both ends and depressed in the middle. 

 The ciliary disk is convex ; the peristome border thick ; cilia very 

 fine and long ; vestibular setae distinct ; contractile vesicle sphe- 

 rical, situated at the extremity of the vestibular cleft ; minute 

 non-contractile vesicles distributed throughout the whole of the 

 parenchyma ; the endoplast is spherical and conspicuous ; endo- 

 plasm granular, and maintains a continual cyclosis or circula- 

 tion. The evertion of the cilia is extremely gradual, occupying 

 about five to ten minutes ; retraction is instantaneous. Mr. W. 

 Saville Kent points out an analogy between the tail-like appen- 

 dage and the telescopic tail of his Yorticella telescopica. It is 

 proposed to bestow the specific title of " caudata " in allusion to 

 this appendage. 



The accompanying woodcut delineates the animal in various 

 aspects, the same being from drawings by myself of the living 

 object, and here greatly magnified. 



Assuming the present form either to be regarded as a species 

 of Gerda or closely allied to that genus, I tentatively draw out 

 the subjoined technical diagnosis. 



