427 



On Distyla spinifera. 



By George Western, F.R.M.S. 



{Read June loth, 1894.) 



Plate XXI. 



This is apparently an undescribed species ; I first found it last 

 spring in some stuff taken on Putney Heath, one or two specimens 

 only, but was unable to find more till a few weeks back, wlien it 

 turned up again somewhat more abundantly, so that now with the 

 help of Mr. Rousselet, who has prepared some slides of it, and of 

 Mr. Dixon Nuttall, to whom I am indebted for drawings, I am 

 able to place it on record. At first sight it rather resembles 

 Metopidia oxysternon, but on closer examination the resemblance 

 is found to be very superficial, and it proves to be a Distyla. In 

 shape it is a long ellipse, the posterior two-thirds protected with 

 a lorica closed behind, abruptly truncated and open in front, but 

 continued by a stiffened membrane forming a sort of double hood 

 for the protection of the head and neck, which are thus capable of 

 entire retraction within the lorica proper. This is divided into 

 two plates with a membranous lateral invagination. The dorsal 

 plate is apparently the smaller of the two. It is depressed, and 

 owing to the presence of a triangular ridge commencing abruptly 

 at the junction of the anterior and middle thirds of its length, and 

 extending almost to its posterior edge, is higher behind than in 

 front. Other ridges and depressions give it a regular facetted 

 appearance. The lower or ventral .shield is hemispherical in 

 transverse section, and has its lateral edges inverted to form the 

 lower plane of the lateral inangulation. On the postero-lateral 

 angles of the edge?, one on either side, are two thorn-like spines, 

 at the base of which are situated the lateral antennae. This 

 striking peculiarity, leading to the easy identification of this 

 Rotifer, I have chosen as the origin of the specific name. The 

 ventral surface is divided into three planes by two longitudinal 

 ridges, extending from the ventral edge and terminating abruptly 

 JouEN. Q. M. C, Series II., No. 35. 30 



