PLYMOUTH NEMERTEANS. 429 



The colour is yellowish pink, interniptecl on the dorsal surface by six 

 longitudinal brown stripes ; the outer lines are confined to the body ; 

 they cease just before the cephalic furrows. On the head, which is 

 narrower than the body and well separated, four dorsal stripes continue. 

 Many eyes are present, arranged centrally in two rows on each side. 

 The cephalic grooves are conspicuously branched and show a brown 

 pigment on the transverse ridges. 



Geographical distribution : Plymouth is the most Northern habitat 

 of this species ; it has not been recorded for any other place in England. 

 D. spcdahilis occurs on the Atlantic coasts of France and at the Cape 

 Verde Islands as well as in the Mediterranean. 



III. Fam. peostomatidae. 



Usually short and slender, somewhat flattened Nemertines with four 

 eyes. Gonads alternating with the intestinal diverticula which are 

 not bifurcated. The oesophageal diverticulum has no pouches. Cerebral 

 organs anterior to the brain. Proboscis with ten nerves. 



Genus Prostoma. 



Usually nearly cylindrical, ventrally somewhat flattened, soft worms. 

 Head sometimes sharply, often however slightly or not at all separated 

 from the body; spathulate or rounded, and often somewhat broader. 

 Nearly always the head shows a characteristic pigmentation. Proboscis 

 with ten nerves. The central stylet and its handle are of equal length ; 

 in the middle the base is narrowed. Only two stylet sacs, containing 

 two to three accessory stylets each. Cerebral organs situated in front 

 of the brain. 



1. Prostoma melanocephalum {Johnston). (Mcintosh. Monogr. 

 T. 2, Fig. 1.) 



Locality : In dredgings from Queen's Grounds and between stones 

 from the Cattewater. 



This species can be distinguished easily from all other Prostomas 

 by the large, intense black spot on the head; this and the yellow 

 colour of the body, in which no traces of brown are to be seen, make it 

 quite impossible to confuse them with P. coronatum, as Beaumont and 

 Eiches have done. Moreover, a great difference in habitus exists 

 between both forms, mature specimens of mdanocephahcm having a 

 length of 30-60 mm. with a breadth of 2 or 2-| mm., while coronatum 

 is one of the slender species of this genus. 



P. melanoceijhaluvi is a shallow-water form, not at all common near 



