BRITISH MARINE TURBELLARIA. 227 



Habitat. — Dredged in 4 fms. off the Duke Rock, Plymouth Sound 

 (F. W. G.). 



Distribution. — Trieste, among Ulva (v. Graff, Bohmig). 

 Family MONOTIDiE. 



Allceocoela with two genital apertures. A spermotheca present. Two 

 germaria and two distinct vitellaria. Testes follicular, closely 

 aggregated between the pharynx and the brain. Pharynx directed 

 posteriorly. An otolith present. Elongate flat forms, with a narrow 

 antenor end, and abroad posterior extremity fur nis/ied with " adhesive 

 cells." 



Genus 23. — Monotus, Diesing.* 

 Monotidce in which the female genital pore lies in front of the male. 



52. Monotus lineatus (0. F. Midler, 2). 



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



1853. Planaria flustr^e, Dalyell (29). 



1861. Monocelis lineata, Claparede (35). 



1861. Monocelis agilis, Claparede (35). 



1865. Typhloplana flustr^e, Johnston (38). 



1875. Monocelis rutilans, 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.t 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 papillse 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 Jiagella. This part of the body is 

 constantly employed during life in active movements in all directions. 



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

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



t A method adopted throughout this memoir. 



