OF CONCHOLOGY 147 



recognized by its beautiful color, very fine, regular ribs, much 

 produced, ventral margin, slender anterior end, bubble-like ele- 

 vations of the epidermis and narrow hinge line. 



It is nearest L. fluctuosa, which has the anterior end broader 

 and more rounded, is compressed, and flattened on the top of 

 the ribs, which are less regular and coarser, the anterior muscu- 

 lar impression being further below the hinge line and the sinus 

 less angulated and proportionately larger. 



MERCBNARIA, Schum. 

 Mercenaria, Schum., Essay, p. 1817. 

 Mercbnaria Kennicottii, n. s. 



Mercenaria Kennicottii, Dall, MSS., 1868. 



Shell cuneiform, dark ferruginous brown, ornamented with 

 fine concentric, slightly elevated lamellae. Valves rather in- 

 flated, thick ; umbones prominent, rounded ; within the anterior 

 third; anterior end rounded from below to the lunule, which is 

 broad, cordiform and impressed, bounded by a deeply incised 

 line. Extreme anterior end of the valves rather pinched to- 

 gether. Anterior ventral margin arcuated. Posterior end 

 thick, rather produced and pointed. Posterior dorsal side 

 roundly arched from the umbones to the end ; two obsolete cari- 

 nas pass from the umbones on each side posteriorly, the inner 

 pair forming the boundary of the ligamentary area. Inner 

 posterior and ventral margin finely crenulated. Hinge line 

 strongly arched behind. Dental area broad, teeth strong. 

 Posterior dental process rugose. Muscular impressions large ; 

 pallia! sinus short, sharply angulated. Sculpture of fine con- 

 centric lamellae, slightly elevated, more so on the anterior end ; 

 more distant on the umbones, thickly crowded near the margin 

 especially anteriorly. Lines of growth prominent at intervals. 

 Lamella passing over the ligamentary area and lunule. Interior 

 white ; the dark brown of the exterior may be a stain but looks 

 natural. Lon. 2-64. Alt. 2-1. Diameter 1*56 in. Angle of 

 the pallial sinus 45°. Lon. of do. *44 in. 



Habitat,— -N eah Bay, W. T., Capt. E. E. Smith. 



I have much pleasure in dedicating this fine species to the 

 memory of the late lamented Robert Kennicott. Two other 

 MSS. names have been applied to it, but my own antedates them 

 both. It is nearest to Venus Stimpsoni, Gould, from Yeddo, 

 Japan, which is a larger species, chalky white, with a lanceolate 

 lunule, long, nearly smooth ligamentary area; much more rounded 

 ventral margin and proportionally much smaller pallial sinus. 



