822 Proceedings of the Royal Irish Academy. 



ColoTor, yellow, pale, or deep apricot yellow, due chiefly to 

 alimentary tract. A patch of opaque white flakes (gland cells) 

 stands out conspicuously on the head between the two pairs of 

 of eyes, and fi'om this in most cases a streak of white runs back 

 along the mid-dorsal line to the tail. 



This is possibly the T. glandidiferuin of Blirger, but the 

 development of opaque white flelds and lines is so uncertain in 

 allied forms as to make one suspicious of its value as a specific 

 character. It is also, except for the absence of any brown 

 pigment on the head, very like T. diadema, Hubrecht. 



(C) On the jSTullipore ground in Port Magee Channel another 

 form was found, possibly a distinct species. These were similar 

 in external featiu-es to certain specimens noted at Port Erin 

 (1895, p. 365), but the central stylet apparatus was diiferent. 

 All the specimens examined (over twenty) were males with well 

 developed gonads, though measuring only from 4-8 mm. in 

 length. 



Body comparatively stout and round ; head also thick and 

 rounded, fairly well marked off from the body ; the cephalic 

 grooves very pronounced. Eyes distinctly large. 



Coloiu", deep orange-red, due largely to orange granular 

 material in the skin. No opaque white on head or body, the 

 head being of the same deep colour as the body. In a few cases a 

 Kttle brown pigment was present behind the anterior eyes on 

 each side. Central stylet apparatus much as in (A). In each 

 reserve stylet pouch three stylets usually present. 

 Tetrastemma melanoceplialuni (Johnston). 



Tetrastemma melanocephalwni^ M'Intosh (1874). 

 Tetrastemma coronatum (?), Hubrecht, Joubin, Burger. 



I shall consider under the head of T. melanocephalum all those 

 Tetrastemmidae with pigment patch on the head. I have 

 examined a very large number, but have failed to assign anj 

 with certainty to the numerous species recognised by Burger. 



The common form everywhere in Valencia Harbour (as also 

 at Port Erin and Plymouth) appears to be the T. coronatum of 

 Hubrecht ; but it does not agree in all respects with Biirger's 

 description. 



The body is slender, an example 20-25 mm. long, when well 

 extended, being less than 1 mm. wide. The head is more or 

 less spathulate in shape, but is more pointed in some individuals. 



