EEPOET ON L.M.B.C. NEMEETINES. 363 



the surface of the body is covered with black pigment, 

 and in no way tends to bridge the gap between the type 

 and T. dor sale. In a few individuals the ground colour 

 is nowhere visible except along a narrow irregular strip of 

 the ventral surface, usually, however, there is a longitudinal 

 median dorsal band free from black pigment, varying 

 much in width in different individuals and frequently 

 interrupted by one or more bridges of pigment ; while one 

 or two examples have been met with in which the black 

 pigment was confined to a series of isolated more or less 

 rounded patches, the aggregate area of which was less 

 than that of the intervening pale surface. 



Tetrastemma immutabile, Riches. 



Two Nemertines agreeing in shape and colour with the 

 description given by Riches were found in 1894 in material 

 from the Clets, and a couple more turned up in shore 

 material from Perwick in 1895. They were from 3 to 6 

 mm. long. 



No intermediate varieties connecting this form with 

 Tetrastemma dor sale were met with. The median dorsal 

 band consists of branched reddish brown pigment cells 

 the processes of which tend to run longitudinally, and 

 also of round granules of darker brown colour, a few of 

 which are scattered over the rest of the dorsal surface. 

 In none were genital organs observed. 



Tetrastemma candidum (0. F. Muller). 



This species was found in considerable abundance 

 inhabiting the weeds between tide-marks at Port Erin, 

 Perwick and Port St. Mary. Very few specimens exceeded 

 1 cm. in length ; the majority were considerably less, yet 

 many even of the smaller ones had well developed genital 

 organs, one male not more than 4 mm. long having G pairs 

 of testes containing ripe spermatozoa. 



These littoral forms, though varying a good deal in colour 



