BRITISH MARINE TURBELLARIA. 215 



animal is securely fixed at will. The epidermis contains numerous 

 rhabdites of a bright yellow colour, to which the tint of the animal is 

 clue. Mouth below, piharynx behind the brain. The pharynx is very 

 small, the musculature being slightly developed. Numerous glands 

 surround it. The intestine occupies the central part of the body, and 

 is enclosed anteriorly by spherical glands. The genital aperture lies a 

 short distance from the hinder end on the ventral surface. The small 

 testes are placed behind the centre of the body in the middle line. The 

 spermatozoa have a very characteristic form. They are divisible into 

 a broad head, and a narrow pointed tail. A dark transverse band 

 separates the head end off as a pointed lid. Down the centre runs a 

 spiral thread. The ova develop from a median cellular mass which, 

 according to Bohmig (57, p. 365), lies close to the brain. In com- 

 pression preparations it is driven posteriorly (PI. XII, fig. 30). The 

 developing ova lie at the sides of the gut. The yolk-glands are paired, 

 large, lobed organs, more or less enclosing the intestine and uniting 

 behind the pharynx. 



Habitat. — In tide-pools, among corallines, Port Erin, Isle of Man 

 (F. W. G.). 



Distribution. — Trieste (v. Graff and Bohmig). 



33. Plagiostoma elongatum, n. sp. 



Length 2 mm. Body cylindrical, stout, elongate, rounded in front, 

 tapering rather suddenly posteriorily. Colour opaque white. Epi- 

 dermis provided with cilia, which are longer anteriorly than elsewhere, 

 and between which stiff flagella occur. Narrow oblong rhabdites are 

 thickly scattered over the surface. They are homogenous and highly 

 refractive. The musculature is strongly developed, and this fact, 

 combined with the opacity of the other organs, renders it a matter of 

 difficulty to examine this species by compression. The mouth is 

 subterminal. Pharynx large, barrel-shaped when at rest, situated 

 behind the brain. It is very muscular, and can extend under and in 

 front of the brain towards the mouth. The intestine is large, cor- 

 responding generally to the form of the body, slightly hollowed in 

 front to receive the base of the pharynx. Tw t o larger irregular black 

 eyes unite by strands of pigment across the brain. The genital pore is 



