144 NUCUL1D.E. 



are devoid of any umbonal ridge, and terminate posteriorly in a 

 rounded peak. 



67. L. frigida, Torell, f. 16S, 169. — "T. ovalis, prope semi- 

 lunaris, subrequilateralis, antice rotundata, postice subrostrata, 

 compressa ; tenuis, diapbana, virescens, nitida, concentrice strio- 

 lata, postice argutius. Margo dorsalis modice convexus, umboni- 

 bus prominulis, ventralis semicircularis, postice obtuse angulatus, 

 leviter impressus; intus opaca, linea marginali albida obducta; 

 denticuli utrinque septem crassiusculi, angulati." — Unable to pro- 

 cure tins Spitzbergen shell (possibly immature, being only the fifth 

 of an inch long), I have copied both figure and description from 

 Torell. 



Sect. III., forming the Subgenus Portlandia. 



68. L. glacialts, Gray, as nf Leach, f. 30, 31 . — T. ovali-acuta, 

 ventricosa, vix hians, a:quilateralis, antice semielliptica, postice 

 obverse cuneil'ormis, cute lutea olivaceo-ilavescente vel olivaceo- 

 tenebrosa induta, rugis minutis arctissimis, undulatis, subgranosis, 

 concentrice lirata. Margo dorsalis posticus vix declivis ; ventralis 

 antice arcuatim acclivis, deinde subretusus, postice subangulatim 

 acclivis. Nates valde eminentes. Regio dorsalis postica magna, 

 late concava. — Peaked oval (at times much produced, at times 

 abbreviated), ventricose, scarcely, if at all gaping, without anterior 

 indented ray, with a rather glossy thin epidermis, that ranges in 

 tint from bright yellow, or yellowish-olive (in the elongated forms) 

 to dusky-olive (in the broader individuals) ; most closely and 

 finely shagreened by raised concentric undulated subgranular 

 wrinkles. Sides equal ; the front unsymmetrically semielliptical, 

 the hinder obversely wedge-shaped, its broad extremity being 

 subtruncated from above inwards. Front dorsal edge just at first 

 horizontal, then more or less arched and sloping : hinder dorsal 

 edge but little sloping, at first somewhat refuse, then convex. 

 Ventral margin arching up in front, subretuse behind the middle, 

 subangular at its junction with the refuse posterior margin. No 

 defined lunule or lozenge, but a wide and large concave hinder 

 dorsal region marked out by an obscure rounded umbonal ridge, 

 the surface before which is somewhat planulate. Cartilage-pit 

 almost perpendicular, not large, triangular (with an arched base). 

 Teeth moderately numerous (ten or twelve) on either side. — The 

 typical or earlier known form is five-sixths of an inch long, and 

 seven lines broad : the elongated variety Porllandica averages 

 eleven-sixteenths of an inch in length and hardly more than three- 



