BRITISH MARINE TURBELLARIA. 203 



Habitat. — Among Fucus, Plymouth Breakwater (F. W. G.). 



Distribution. — Naples (v. Graff). 



I append a query to this species, since my observations were made 

 on one specimen, and agreed more closely (but not entirely) with M. 

 neapolitanum than with any other species. More specimens of this 

 marine Mesostoma are greatly needed, as its position is not thoroughly 

 denned. 



Family PROBOSCID^. 



Rhabclocoela with tactile proboscis ; one or two genital pores, Germaria 

 and vitellaria distinct. Testes compact. A spermotheca present. 

 Mouth ventral. Gut discontinuous in the adult, owing to the 

 development of the gonads. Copulatory organ complicated, chitinous 

 (v. Graff, p. 315). 



Subfamily PSEUDORHYNCHINiE. 



Proboscis without sheath or muscular cone. Retractors represented by 

 short muscular bundles. Pharynx rosidate. One genital pore. Two 

 germaria. Yolk-glands reticular. Testes paired, rounded. 



Genus 11. — Pseudorhvnchus, v. Graff, 



20. PSEUDORHYNCHUS BIFIDUS (Mcintosh). 



1875- Mesostomtjji bifidum, Mcintosh (45). 

 Length 1 *3 mm. Body convex dorsally, flat on the ventral surface, 

 slightly expanded towards the posterior end, which is bifid. The conical 

 anterior extremity (proboscis) is devoid of cilia. Colour pale orange 

 with darker spots, the proboscis colourless. Ehabdites are well 

 developed and of three kinds (Jensen) — straight, ovoid, and needle- 

 shaped. Strong adhesive papillae occur at the bifid hinder end. 

 Pharynx subcentral. The genital pore is placed behind the middle. 

 Testes small, rounded. Vasa defer entia unite in a vesicula, which 

 opens, along with the ducts of " granule-glands," into the proximal 

 swollen parts of the penis. The distal portion is muscular, and 

 contains the copulatory organ. The latter is a conical chitinous tube, 

 the outer wall of which is produced into a series of spiral ridges 

 running from the base to the apex in a screw-like manner. The usual 



