NO. 1139. DEEP-WATER MOLLUSCAVEERILL .i\I> 7.T.SJJ. 863 



W. long. 69 1'2'. and K lat. 35 12' 10", W. long. 74 57' 15", in 22 to 

 516 fathoms, 1872-1885. 



The most prominent character of this species is the relatively lar^e 

 si/e of the cartilage-pit which intersects both the hinge- margins and 

 the beaks and is therefore plainly visible from the exterior. In outline 

 it is similar to 1". iris and Y. in flat a but is more pointed and narrower 

 posteriorly than either of them. They differ also in having much 

 smaller cartilage-pits and in the number of the teeth. 



Specimens formerly identified as Yoldia obem Stimpson, agree per- 

 fectly with authentic specimens of lucifla sent by Doctor Friele from 

 Spitzbergeu. As none of the species known to us agree sufficiently 

 well with the description and figure of Lerta obem Stimpson, for us to 

 decide definitely as to its correct position, unless we are to consider 

 the figure a very incorrect representation, we prefer to let it remain 

 doubtfully, as a synonym of Y. lucid tt, where Jeffreys and others have 

 placed it. 



YOLDIELLA IRIS, new species. 

 (Plates LXXX, figs. 1, 2; LXXXII, fig. 11.) 



Shell small, thin, rather delicate, long-ovate or ovate-elliptical, with 

 the beaks in front of the middle, not much swollen; surface smooth, or 

 nearly so, with brilliant iridescence. The autero-dorsal margin is con- 

 vex and slightly arched, sloping gradually to the obtusely rounded 

 and slightly produced anterior end; ventral margin very broadly and 

 evenly curved; posterior end obliquely ascending, obtusely pointed or 

 rounded at the tip with a slight dorsal angulation; postero-dorsal mar- 

 gin slightly convex, sloping but little, pinched up into a thin, rather 

 prominent keel. The urnbos are small and prominent with the beaks 

 small, curved inward and backward, closely appressed to the margin. 

 The epidermis is grayish or greenish yellow, smooth and shining; the 

 surface is brilliantly iridescent, covered with faintly marked, fine, con- 

 centric lines, most distinct near the ventral margin and anteriorly; 

 under the lens these appear like faint, close undulations over most of 

 the surface. Escutcheon defined by a well-marked depression. 



The hinge-margin is thickened and forms a very obtuse angle at the 

 beaks; the posterior portion which is only slightly curved distally is 

 longer than the anterior which is nearly straight. In the largest speci- 

 mens there are twelve or thirteen acute erect V-shaped teeth in each 

 series, including one or two minute, proximal ones. The resilial pit is 

 minute, situated on the inner face of the thin edentulous hinge-plate, 

 beneath the beaks, and faces ventrally so that it is scarcely visible in a 

 front view and but partially interrupts the hinge-plate. Outside the 

 series of teeth, on both sides of the beak there is a smooth, raised 

 margin. 



Length of one of the larger specimens, 7,~> nun.; height, 5 mm.; from 

 beak to posterior end, 4.5 mm. 



