BRITISH MARINE TURBELLARIA. 487 



Genus 23. — Monotus, Diesing.^ 



Monotidae in which the female genital pore lies 

 in front of the male. 



52. MoNOTus LiNEATUs (O. F. MUUer, 2). 



1773. Fasciola lineata, 0. F. Miiller (2). 



1853. Planarta flustr^, Daly ell (29). 



1861. MoNOCELis LINEATA, Claparede (35). 



1861. MoNOCELis AGiLis, Claparede (35). 



1865. Typhloplana FLUSTEiE, Johnston (38). 



1875. MoNOCELis RDTiLANS, Mcintosh (45). 



1882. MoNOTus LINEATUS, V. Graff (53). 



This synonymy refers merely to the works of authors who 

 have described British examples of this species.^ For a fuller 

 list see v. Graff (53), p. 418. 



Length 2 — 2-5 mm. Body very elongate, appearing to 

 the naked eye as a fine white thread. The hinder end assumes 

 the form of a disc when the animal contracts. By means of 

 adhesive papillae present on the surface of this " Haftscheibe " 

 it clings very tenaciously to the substratum. Colour variable, 

 sometimes absent, more frequently present in the form of 

 brown or grey reticular pigment. The epidermis of the 

 anterior end is markedly thicker than elsewhere, and bears 

 numbers of well-developed sensitive flagella. This part of 

 the body is constantly employed during life in active move- 

 ments in all directions. Should it meet with an obstacle it 

 retracts with amazing rapidity. The rhabdites are only feebly 

 developed. Owing to the great contractility of the body the 

 positions of the organs are difficult to define. Considering, 

 however, the animal to be in a fully extended state, the mouth 

 is a short distance behind the centre of the body. The 

 pharynx is cylindrical, very muscular, its proximal end being 

 almost central. The gut is extensive; when contracted it 

 becomes distinctly sacculated. In the middle line anteriorly 



1 Diesing, K. M., "Revision d. Turbellaria, Rhabdocoelen," 'Sitzungb. d, 

 Akad. Wien,' Bd. xlv, 1862, p. 211. 



* A method adopted throughout this memoir. 



