264 NEW FOSSIL SHELLS 



Remarks. The carina on the last whorl is very large. There is a corresponding 

 depression in the interior of the mouth. Occasionally, there is an angulated line near 

 the suture of the last whorl, but this is not a constant character. The carina is rather 

 nearer the apex than the base of the shell. The substance is exceedingly thin, and has 

 somewhat the appearance of ivory. On a front view, the general outline of the shell has 

 a remarkably rhomboid al shape. 



I know of no species of Rotella, except the following, which resembles this beautiful 

 little shell. 



R. LENTICULARIS, PL. 36. FIG. 79. 



R. testa lenticulari, depressd, tenui, Icevi, politd; spird brevissimd, sub-ovatd, obtusa; suturis parvis, linearibus; 

 anfractibus quatuor, convexis; anfractu ultimo angulato; basi Icevi; callo parvo; aperturd sub-rotunda; columelld lata. 

 curvatd. 



Shell lenticular, depressed, thin, smooth, polished; spire very short, sub-ovate, obtuse; sutures small, linear; 

 whorls four, convex; last whorl angulate; base smooth; callus small; mouth sub-rotund; columella broad, curved. 



Length .04. Breadth .09 of an inch. 



Remarks. The angle on the last whorl is very variable. It sometimes amounts 

 almost to a carina. The mouth is nearly round. The callus is slightly depressed 

 below the surrounding surface. 



This shell is, in part, allied to both the preceding species, but differs in the number 

 of whorls, shape of the columella and spire, and the angle on the last whorl. They 

 also differ much in thickness. 



R. UMBILICATA, PL. 36. FTG. 80. 



12. testa orbiculari, valde depressd, crassd, Icevi, politd; spird umbilicatd; anfractibus occullis; anfractu ultimo ro- 

 lundato, spiram tegente, ad suturam superiorem lined parvd impressd transversd; basi Icevi; callo magno, tenui, medio 

 depresso; aperturd rotunda; columelld latissimd, subsulcatd. 



Shell orbicular, very much depressed, thick, smooth, polished; spire umbilicate; whorls concealed; last whorl 

 rounded, covering the spire, with a small impressed transverse line near the superior suture; base smooth; callus 

 large, thin, depressed in the middle; mouth rotund; columella very wide, sub-sulcate. 



Length .05. Breadth .10 of an inch. 



Remarks. The columella has a shallow groove in its centre. The mouth is almost 

 round. 



This little shell, in general outline, is not unlike the R, nana, Lea, but the peculiar 

 umbilicated spire will at once distinguish them. 



This genus is quite rare in a fossil state. I believe that but one, the R. suturalis, has 

 been found in the Tertiary beds of Europe. In this country the species appear to be 

 more numerous. 



GENUS TROCHUS. 

 T. ARMILLUS, PL. 37. FIG. 81. 



T. testa conicd, elevatd, crassiusculd, imperforatd, costatd, striatd; spird conicd, acuminatd; suturis minimis; n- 

 fractibus quinque, plants; costis transversis, tribus, noduliferis, alternantibus striis minimis; anfractu ultimo acute 

 angulato, carinato; basi valde planulato, striis magnis et parvis; aperturd quadrilaterali. 



