BRITISH MARINE TURBELLARIA. 207 



23. Macrorhynchus croceus (Fabricius, 9). 



Length 1*5 mm. Body reddish, swollen posteriorly, pointed in front, 

 where it is nearly white. Prooboscis very powerfully developed. Of the 

 parts composing the genital apparatus, the most diagnostic is the 

 copulatory organ. At its proximal cylindrical end it receives the 

 secretions of the vesicula seminalis and granule-reservoir, which are 

 contained in an elongate sac strengthened by spirally-arranged muscles. 

 The distal portion is spirally twisted, and consists of two canals, 

 each containing a part of the continuation of the proximal single 

 cavity. The upper edge of this spiral is "toothed." The egg-capsule 

 is stalked. Several points, such as the relations of the germ- and 

 yolk-glands and the presence of a spermotheca, are not yet satisfactorily 

 determined. 



Habitat. — Among Fucus and Laminaria below the surface of the 

 sea. Millport (v. Graff) ; Plymouth (F. W. G.). 



Distribution. — Apparently abundant in the northern seas. West 

 coast of Greenland (Levensen) and of Norway (Jensen), Fai-oe 

 Islands (Schmidt), Denmark (Oersted), Wimmereux (Hallez). 



Among the Macrorhynchus collected at Plymouth were two species 

 apparently new. Since, however, my observations are incomplete, I 

 will not further describe them than by saying that one species closely 

 resembled M. mamertinus, v. Graff, in the form and position of its 

 gonads. The pharynx was not so strongly developed. 



ii. Venenosi. 



24. Macrorhynchus heligolandicus, Metschnikoff (37). 



Length *5 — 1*5 mm. Body rounded at both ends, cylindrical, white, 

 sometimes with brown spots. The proboscis is typical but small. 

 The bilobed brain bears lenticulate eyes. The pharynx is rather 

 small, placed as far in front of the centre of the body as the genital 

 pore is behind it. The reproductive organs were first described by 

 Jensen. The great variability of certain (especially the chitinous) 

 parts, their complexity, and the presence or absence of certain 

 accessory organs (spermotheca, &c.) according to the particular stage 

 of development, render this perhaps the most difficult of all Turbellaria 



