BRITISH MARINE TURBBLLARIA. 223 



behind. Eyes absent. For further details and figures see v. Graff, 

 'Monogr.,' p. 404, and pi. xix, figs. 15 — 17. 



Habitat. — A specimen at Millport in a tide-pool (v. Graff). 



v. Graff described this form as the only blind Plagiostomid. I have, 

 however, found a probably new species of Plagiostoma in which the 

 eyes were wanting. 



Genus 20. — Allostoma, van Beneden (33). 



Allostomince in which the " circular furrow " at the level of the brain is 

 provided ivith long cilia. 



47. Allostoma pallidum, van Beneden (33). 



Length 2 mm. Body cylindrical, tapering slightly towards each 

 extremity. The anterior sixth is sharply separated from the rest of 

 the body by a transverse marking, the nature of which is not quite 

 clear. It is probably due to the ciliated " circular furrow." Colour 

 yellowish white. The epidermis contains numerous pseudo-rhabdites. 

 Considering rhabdites as a condensed glandular secretion, pseudo- 

 rhabdites are intermediate between the amorphous secretion and 

 rhabdites. The mouth is posterior; the pharynx short, leading into 

 an extensive gut. v. Graff has described the genital organs fully. 

 Testes surround the brain. Vasa defer entia convey the sperm in balls 

 to the base of a pyriform penis, in front of which lie the ovaries. The 

 oviducts unite and open through the subterminal genital pore. Yolk- 

 glands lateral, lobed. (See v. Graff, 'Monogr.,' pi. xxix, figs. 12 — 14.) 



Habitat. — Millport (v. Graff). 



Distribution. — Ostende (van Beneden, v. Graff). 



Van Beneden (33) has described the oval egg-capsules, which are 

 very small, and extruded one at a time. The young when hatched 

 are without a definitive pharynx, gut, eyes, or brain. They become 

 sexually mature in three weeks. 



Subfamily Cylindrostomin^e. 

 v. Graffs definition of this sub-family (' Monogr., p. 409) has been 



