826 Proceedings of the Royal Irish Academy. 



organs, and greatly developed head gland; and by being mostly 

 bermaplii'odite. The jSTemertine under consideration fails to 

 conform witb this diagnosis in every particular ; the eyes are 

 as in Tetrastemma, the cerebral organ is well developed, the 

 head gland is small, and the sexes are separate. In fact, there 

 is no doubt that it belongs to the Tetrastemmidse, and to the 

 genus Tetrastemma, since the shape of the stylet handle of the 

 central stylet can hardly be reckoned of generic importance. 

 In general appearance my specimens resemble Burger's coloui-ed 

 figure of T. cephalophorum fairly well, and they agree in most 

 respects with his somewhat brief description. But there are 

 points of difference which, if constant, would entitle the British 

 form to separate specific rank. Burger's diagnosis, however, is 

 open to the suspicion of being based, as in the case of several 

 of his new species, on a single specimen, and I am accordingly 

 loath to add another species to an already overburdened genus. 

 The points of difference are these : — The head of the British 

 animal, though well marked off fi'om the body, and approaching 

 a rhomboid in outline, is much more rounded usually than 

 represented by Biirger ^op. cit. pi. iii., fig. 22), and is distinctly 

 notched in front (the notch becoming much accentuated in 

 contraction). One individual, however, approximated very 

 closely in form of head to Biirger's figui'e. The body is rounded 

 (in section) and stout, as Burger's describes, but he gives the 

 width of a 15 mm. example as If mm., while an individual, 

 22 mm. in length, measured by myself, was not more than 

 1^ mm. thick when fully extended. However, his statement 

 is hardly borne out by his di'awing. A more important 

 difference is found with regard to the central stylet apparatus. 

 Biirger describes and represents in a somewhat indifferent figure 

 (pi. xxix., fig. 42) the central stylet of T. ceplialopliorum as thin 

 and long, approaching the handle in length. I have examined 

 this structure in a number of individuals of the British form (over 

 20). The handle is long, and has the characteristic flat-based 

 conical form like T. cephalophorum ; but the stylet is short and 

 stou+, averaging about half the length of the handle, though 

 with a fairly wide range of variation. Other points are the ex- 

 tension of the reddish brown pigment, which covers the body, on 

 to the dorsal surface of the head as far as the anterior furrows ; 

 ^nd in front of these, the conspicuous development of opaque 

 white flakes (gland cells) which are scattered in some cases 



