DESCRIPTIONS OF SPECIES. 



Marseniad^:. 

 Marsenia, Leach. 



The genus Marsenia proper was established by Leach as early as 1820. These 

 animals are not of large size. The mantle, which is closed above, has a broad border, and 

 there is only one sub-pallial respiratory fold and furrow, lying anteriorly, and leading into 

 the left side of the branchial opening. The calcareous shell, which is entirely inclosed, 

 has a small spiral with a somewhat wide opening, and with a distinct columellar sinus. 

 The Marsenice have large, lancet-shaped branchial leaflets, which are covered laterally 

 with transverse folds. The mandibular plates are strongly developed, and composed not 

 of rows of rods, but of a tolerably uniform (homogeneous) mass, with a broad biting 

 or chewing margin. The median tooth plates of the tongue have their posterior margin 

 almost always deeply cleft ; the strong lateral plates have their hook denticulated on each 

 margin, but unequally toothed. There is always a large proventriculus. The sexes are 

 separate ; the inferior portion of the vas deferens is quite free, partly covering with its 

 coils the bulbus pharyngeus and the foliated stomach. The flattened, sickle-shaped 

 penis is somewhat broadened terminally. 



The true Marsenice occur in all seas, both tropical and arctic. But little is known of 

 their general biological relations. The ontogeny of a typical form has been partially 

 followed. 1 



Marsenia dubia, n. sp. (PI. I. figs. 1-6). 

 Habitat. — Eastern North Atlantic, off Cape Verde. 



Only one specimen (a male) was found, on the 28th July 1873, near St Vincent, Cape 

 Verde. 



This small form measured 45 mm. in length, about 4 in breadth, and 175 in height. 

 The general colour was whitish, aud the yet whiter shell shimmered through the dorsal 

 surface. Inform it agreed with the typical Marsenice; the respiratory fold of the mantle 



~1 1 Cf. also my monograph of the Marseniadse, which will shortly appear (1886, 1887), as Supplement III. 

 to my Malacologieal Researches, in Semper's Account of his Travels in the Philippines : Reisen im Archipel^d. 

 Philippinen, &c. 



