254 NEW FOSSIL SHELLS 



FAMILY NERITID^E. 



GENUS NATICA. 

 N. APERTA, PL. 36. FIG. 51. 



N. testa oblique ellipticd, tenui, costulatd, sub-striatd, perforatd; spird depressd, ovatd, obtusd, prope apicem leevi; 

 suluris parvis, linearibus; anfractibus quatuor, convexis; costulis transversalibus, crebris, plants, quadrangularibus; 

 sir/is longitudinalibus, minutissimis ; anfractu ultimo ovato; basi oblique costulald; perforatione parvd, angustd; 

 apertura maxima, superne sinuatd, inferne ellipticd. 



Shell obliquely elliptical, thin, costulate, snb-striate, perforate; spire depressed, ovate, obtuse, smooth near the 

 apex; sutures small, linear; whorls four, convex; costulae numerous, transverse, quadrangular, flat; striae longitudinal, 

 very small; last whorl ovate; base obliquely costulate; perforation small, narrow; mouth very large, sinuate above, 

 elliptical below. 



Length .70. Breadth .62 of an inch. 



Remarks. The costulse are small, wider than the spaces between them, and very 

 numerous. The longitudinal lines of growth are exceedingly minute; so much so as to 

 be invisible to the naked eye. Both ribs and striae become obsolete on the upper whorls, 

 so that the two or three nearest the apex are smooth. The mouth is somewhat lunate, 

 contracted above and expanded below. The umbilicus is small, and nearly concealed 

 by the columella. 



This shell is closely allied to the N. fragilis, Conrad, and it is with some hesitation 

 that I separate it. It, however, differs in the ribs, the umbilicus, and the shape of the 

 mouth. 



N. SPH^ERULUS, PL. 36. Flo. 52. 



N. testa globoso-acuminatd, obliqud, tenui, Icevi, politd, imperforatd; spird breviusculd, sub-conicd, acutd; suturis 

 parvis, impressis; anfraclibus quatuor, sub-convexis; anfractu ultimo rotundato; basi leevi; umbilico occulto; callo 

 semicirculari, lined, impressd marginato; apertura semi-ovatd; columella recta, superne incrassatd. 



Shell globosely acuminate, oblique, thin, smooth, polished, imperforate; spire rather short, sub-conical, acute; su- 

 tures small, impressed; whorls four, somewhat convex; last whorl rounded; base smooth; umbilicus hidden ; callus 

 semicircular, margined by an impressed line; mouth semi-ovate;. columella straight, incrassated above. 



Length .12. Breadth .11 of an inch. 



Remarks. This shell is too small and perfect to be the young of so large a species as 

 N. dnplicata, which it resembles. Out of twenty or thirty specimens the admeasure- 

 ments given above were the largest, the others decreasing to a size scarcely visible with- 

 out a microscope. The only other species to which it is allied is the N. percallosa, 

 Conrad, but the small size and more elevated spire distinguish it. 



N. CRASSILABRUM, PL. 36. FIG. 53. 



N. testa transverse ellipticd, depressd, crassd, l<evi, politd, imperforatd' spird cornea, obtusd, valde depressd; suhiris 

 profundis, linearibus; anfractibus quatuor, convexis, superne planulatis; anfractu ultimo rotundato ; basi Icevi: um- 

 bilico occulto, parvo; apertura sub-rotunda; labro superne valde incrassato. 



Shell transversely elliptical, depressed, thick, smooth, polished, imperforate; spire conical, obtuse, very much de- 

 pressed; sutures deep, linear; whorls four, convex, flattened above; last whorl rounded; base smooth; umbilicus 

 hidden, small; mouth sub-rotund; outer lip much thickened above. 



