BRITISH MARINE TUHBELLARIA. 191 



thus : — From the anterior end backwards for one-third of its length 

 the margins of the body are capable of being gradually extended 

 outwards, so that the greatest width of these animals when in motion 

 is a short distance in front of the centre of the body. These lappets 

 are then flapped inwards and downwards, the animal at the following 

 instant leaping forward. When, however, contraction occurs, it is no 

 longer possible to define the lappets. The anterior end is at a much 

 lower level than the rest of the dorsal surface. As the change of level 

 is abrupt the front end appears snout-like, especially when seen from 

 the side. This snout is moved from side to side in a sensitive manner. 

 Short cilia and slightly irregular rhabdites are present in the epidermis, 

 and are disposed in alternate longitudinal rows, which converge 

 anteriorly towards the opening of "■frontal gland.' 1 Eyes are absent. 

 The otolith is concavo-convex, with a central "nucleus." The two 

 genital yores are posterior, the female in front of the male. Opening 

 to the exterior through the former is the spermotheca. The curved 

 penis receives the contents of the seminal vesicle. 



Habitat. — In tide-pools, Millport (v. Graff). Two specimens 

 among Zostera and Corallina, Plymouth (F. W. G.), 



6. Convoluta paradoxa, Oersted (16), 1884. 



1777. Planaria convoluta, 0. F. Muller (4). 



1844. Convoluta paradoxa, Oersted (16). 



1845. Planaria macrocephala, Johnston (20). 

 1S53. ,, haustrum, Dalyell (29). 

 ]S55. Convoluta paradoxa, Gosse (30). 



1861. ,, „ Claparede (35). 



1865. ,, ,, Johnston (38). 



1866. ,, ,, Lankester (39). 



Length 1 — 3*5 mm. Schmidt (28) found specimens up to 9 mm. in 

 length in the Faroe Islands and other northern localities ; v. Graff 

 records equally large examples from Millport. Specimens from more 

 southerly places are usually much smaller, and it might therefore 

 appear that this species attains a larger size in the northern than in 

 the southern seas. Claparede, however (35), working on the north- 

 west coast of Skye, examined a large number of specimens, none of 

 which exceeded 2 mm. in length ; while recently (55) v. Graff has 

 found "giant specimens" at Posscoff. It seems more likely, as 



