NE.ERA. 49 



valve, and a slight lateral on the posterior side of the right 

 valve : inside glossy and nacreous ; posterior side separated by 

 a sharp rib : scars indistinct. L. 0*8. B. 0-4. 



Habitat : Loch Fyne (M' Andrew and Barlee) ; Skye 

 and Shetland (Barlee) ; in 40-75 f., on a muddy 

 ground. Fossil in the Belgian tertiaries (Nyst). Its 

 known distribution elsewhere in a recent state is as 

 follows : — Bohuslan (Loven) ; Christiania, 40-100 f. 

 (Asbjornsen) ; Bergen, 40-50 f. (Danielssen) ; Fin- 

 mark (Sars and Lilljeborg) ; dead valves in the iEgean, 

 75-105 f. (Forbes) . 



It is the N. vitrea of Loven. 



2. N. costella'ta*, Deshayes. 



Corbala costellata, Desh. Exp. Scient. Mor. (Geologie) p. 86, t. vii. f. 1-3. 

 N. costellata, F. & H. i. p. 199, pi. vii. f. 8, 9, and (animal) pi. G. f. 8, 9. 



Body gelatinous, clear white : mantle so transparent as to 

 allow the pink gills and dark brown liver to be seen through 

 it : tubes cylindrical, sometimes yellow with reddish or orange 

 markings, and tinged with brown at their extremities; ex- 

 cretal tube much the smaller of the two ; tentacular cirri white 

 and plain, extending beyond the tubes ; orifices fringed : foot 

 narrow. 



Shell more slender than N. abbreviate, more ineqnivalve, 

 much less ventricose and even somewhat compressed, equally 

 fragile, semitransparent, glossy and iridescent : sculpture. 

 20-30 longitudinally radiating ribs, which are slighter and 

 more like striae on the anterior side and in front, but stronger 

 and more distant towards the posterior side, especially the last 

 two or three ; these ribs vary in size and fineness ; the pro- 

 longed part on the posterior side is also marked with two or 

 three slight ribs, which are parallel with the dorsal line and 

 extend to the rostral point : colour and epidermis as in the 

 species last described : margins also similar, except behind, 

 where the anterior dorsal margin is raised and appears high- 

 shouldered, and the posterior dorsal margin is inflected and 



* Fine-ribbed. 

 VOL. III. D 



