BRITISH MARINE TURBELLARIA. 229 



known (Aplysia, see Garstang, 'Journal Marine Biol. Assoc.,' N.S., 

 vol. i. No. 4, p. 411); and in this case the change in colour appears to go 

 hand in hand with a change of surroundings. Pharynx, brain, otolith, 

 and eye as in M. lineatus. The male pore is placed further forward 

 than in the latter species. The vasa cleferentia open into the neck of 

 the very muscular vesicula seminalis. The copulatory organ is a 

 hollow chitinous spine of variable shape, connected at its base by 

 muscles to the wall of the seminal vesicle. Numerous accessory 

 glands open at this level. The spermatozoa are whip- shaped, the 

 handle being stout, the lash a very fine thread. Opening to the 

 exterior through the female genital pore is the spermotheca, provided, 

 according to v. Graff and Jensen, with secondary lobes. The remaining 

 parts of the female genital apparatus do not materially differ from 

 those of M. lineatus. 



Habitat. — This species extends its range to the higher parts of the 

 littoral zone. In consequence it is liable to be exposed to the air for 

 some hours. Many of its devices for obtaining a moist position 

 during ebb-tide have been described by Hallez and v. Graff. Thus the 

 former observer collected Balani, the latter Chitons and Patellar at 

 low tide. After placing these in sea water, Monotus fuscus crept out 

 of gills or thoracic limbs as the case might be. In the Isle of Man I 

 have found them nestling among the appendages of Balani. Millport 

 (v. Graff) j Port Erin, and Plymouth (F. W. G). 



Distribution. — Faroe Islands) Schmidt, 24), Bergen (Jensen, 49), 

 Drobeck and Denmark (Oersted, 16), Heligoland (v. Graff), Cuxhaven 

 in the Baltic (Schultze), Ostend (van Benedin [33] and v. Graff). 

 Wimmereux (Hallez, 50). 



54. Monotus albus, Levinsen (51). 



Length \S mm. (i.e. half that of Levinsen's specimen). Body 

 elongate, narrow, the hinder end not expanded into a disc, colourless ; 

 the contents of the gut reddish. Ocular pigment absent. Pharynx 

 posterior. A large spermotheca containing a refractive secretion opens 

 to the exterior iu front of the penis, which is armed with a shoe- 

 shaped chitinous copulatory organ, bearing a couple of lateral teeth on 

 the free margins. 



