BRITISH MARINE TURBELLARIA. 501 



Leptoplana alcinoi and vitrea its walls are very muscular, 

 and the organ becomes a bursa copulatrix. External form and 

 colour, as Lang has forcibly stated (54, p. 482), afford no secure 

 basis for the foundation of characters by which the species of 

 Leptoplana may be distinguished. 



63. Leptoplana Mertensii (Claparede). 



1861. Centrostomum Mertensii, Claparede (35). 



Length 18 mm. Body oval, white or yellowish. Two 

 groups of eyes on the dorsal surface. 



As no details as to the structure of the genital organs are 

 given, it is impossible to satisfactorily assign a position to this 

 species. 



Habitat. — On Laminaria, Lamlash Bay, Arran (Claparede). 



APPENDIX TO LEPTOPLANIDiE. 

 64. Planaria atomata, O. F. Miiller. 



1777. Planaria atomata, O. F. Miiller (4). 



1823. „ „ Fleming (8). 



1839. „ „ Forbes and Goodsir (13). 



1844. Leptoplana atomata, Oersted (16). 

 ? 1845. „ Driebachensis, Oersted (21). 



? 1853. Planaria maculata, Dalyell (29). 



1865. Leptoplana atomata, Johnston (38). 



1874. „ „ Mcintosh (45). 



Length 10 — 12 ram. Body oval, slightly wider in front 

 than behind, rounded at both extremities. Colour variable, 

 the ground-tint white or brown, spotted with reddish-brown, 

 white beneath. Ova are seen as white dots over the upper 

 surface. Two " tentacular" and two cephalic groups of eyes 

 are present. The only known fact about the genital organs is 

 that the penis has a bulbous base, and a transparent terminal 

 duct which contains a hard stylet. 



Habitat. — Coast of Scotland (Fleming) ; Orkneys and 



