76 N. ODHNER, NORTHERN AND ARCTIC INVERTEBRATES. VI. PROSOBRANCIIIA. 2 SEMIPROBOSCIDIFERA. 



Vtariation: 



Osphradiuin and foot are constant; in the specimen from West Greenlandthelatter 

 has slightly projecting anterior corners, but generally tliese are broadly rounded. The 

 radula has always a denticulated inner uncinus; no exception was discovered, though 

 nearly all the specimens were examined; in the specimen from Horn Sound 3 uncini were 

 present on each side, the outermost ones minute but well developed, especially on the 

 left side of the radula. 



General Remarks on the Genus Onchidiopsis. 



Our present knowledge of the genus Onchidiopsis is almost entirely based upon 

 the excellent works of Rud. Bergh about the anatomy of O. groenlandica and O. gla- 

 cialis, which were for the first time distinguished by him in 1886 — 87. Though the char- 

 acters originally described as specific ha ve been found here to be subject to some varia- 

 tion, both the forms, judging from other characteristics, appear to be well-distinguished 

 species. To these two in 1897 Locard added a new form, O. aurantiaca, dredged by 

 the Travailleur Expedition in the Gulf of Gascony, and in 1910 Balch described a new 

 species, O. corys, from the Labrador coast. Lastly, in the present work a further species 

 is established, O. latissima. 



O. aurantiaca Locard must, however, be removed from the genus and placed among 

 Lamellaria (or allies), judging both from the figure and from the description given by 

 Locard. He says namely (P. 485): »la coquille interne était entiérement brisée» and 

 »bord continu, légérement aminci, avec un pH accusé au iiiveau de la tete». 



The main organisation of the genus is known from the works of Bergh (1886 — ■ 

 87), dealing with the anatomy of O. groenlandica and glacialis. Here the genus is described 

 as hermaphrodite, which has been since confirmed by Pelseneer (1895), and the whole 

 organisation has been closely investigated, so that little remains to be added. Some 

 comparisons of the species as to their exteriör habitus may be given here and also some 

 points of view as to the systematical relations of the genus. 



By the mantle, the authors usually mean the outer covering of the body, conceal- 

 ing the shell. From the presence of an inspiratory and an expiratory fold in its front 

 and right margin, this »mantle» is evidently homologoiis to the outer or secondary 

 mantle-margin in Marsenina, which in Onchidiopsis has become expanded and has coalesced 

 all över the shell. The upper or primary mantle-border, as in Marsenina and Velutina, 

 is attached closely to the shell-margin; together with the marginal muscle-band it forms 

 the »Schalenleiste» of Bergh, which »meistens aus 2 — 3 Bändern zusammengesetzt 

 scheint» (Bergpi 1887, P. 266). The shell-muscles appear somewhat above these bands 

 and they are also band-like. 



In O. glacialis and groenlandica the mantle börder surrounds the shell-bearing por- 

 tion of the back in the form of a complete ring. The shell-muscles of both sides are con- 

 tinuous posteriorly in each other; anteriorly they widen somewhat and terminate in 



