MUSEUM OF COMPARATIVE ZOOLOGY. 113 



centric ridges, hardly rising to lamella? except posteriorly, covering the entire 

 shell, averaging six to a millimeter but more crowded toward the basal mar- 

 gin and especially on the rostrum where they are also most elevated ; a single 

 faint ridge extending from the umbo to the lower corner of the rather square- 

 ended rostrum, which ridge is formed by a slight elevation of the lamella? 

 where they change from longitudinal to transverse following the lines of 

 growth ; there is also a faint inward fiexuosity in the lamella? and basal margin 

 in advance of this where the rostral indentation occurs in most species ; ante- 

 rior cardinal margin gently rounded, anterior end rounded to the rather 

 straight base which is hardly interrupted by the fiexuosity above mentioned ; 

 posterior cardinal margin rather concave ; rostrum rather squarely truncated, 

 nearly straight ; within polished ; cardinal border thin ; ligamentary fossette 

 extremely small, narrow, oblique, and not projecting within the margin. 



Lon. 11.5 mm., of which 5.0 is forward from the line of the umbo ; alt. 5.0 ; 

 diam. (approx.) 5.0 mm. 



Station 44, 539 fms., one right valve. 



This, from the descriptions, is clearly not one of the species obtained by Jef- 

 freys, and is not like any of those figured by Sars or in the monographs. 



Neaera arcuata n. s. 



Shell very thin, white, polished, the basal margin evenly arcuated from the 

 anterior end to the lower angle of the extremity of the rostrum ; anterior car- 

 dinal margin parallel with or hidden by the oblique anterior slope from the 

 umbo ; posterior cardinal margin concavely arched ; rostrum short, somewhat 

 recurved, roundly truncated at the tip, not differentiated by any riblet and 

 with a very small triangular space of transverse wrinklings ; sculpture of rather 

 distant (four to the millimeter) concentric flattened threads slightly sharper 

 and more closely set toward the ends and quite faint on the umbo and in 

 the middle of the shell ; intercalary lines of growth so faint as not to be per- 

 ceptible ; there are some radiating opaque white color lines on the general 

 translucent ground, but no radiating sculpture ; interior brilliantly polished ; 

 margins very thin, not reflected; ligamentary fossette oblique, small, narrow, 

 projecting within the margin ; posterior extremity of the rostrum slightly in- 

 flated or twisted to the left. Lon. 12.5 (the umbo exactly in the middle of 

 the shell) ; alt. 7.3 ; diam. (approx.) 5.5 mm. 



Yucatan Strait, 640 fins., one left valve. 



By its evenly arcuated base, want of dill'.' initiated rostrum, and peculiar 

 sculpture, this species seems to be sufficiently distinguished. 



Necera lamellifera n. 8. 



Shell thin, inflated, not polished, white, short, and ornamented with about 

 thirty-three thin sharp elevated and slightly reflected concentric lamellae ; the 



VOL. IX. — NO. 2. 8 



