696 Modification of the Apex in Gastropod Mollusks. 



IVassa vilbex Say. 



The apex is like that of glans, the same number of whorls, ex- 

 cepting that its color is 3'ellowish-white. A dozen specimens ex- 

 amined. 



JVassa incrassata Gmelin. 



Apex like that of trivittata, the same number of whorls, color 

 white in some specimens and wine-colored in others. Five speci- 

 mens examined. 



TVassa tegula Eeeve. 



Apes like those of trivittata and incrassata, the same number of 

 whorls which are wine-colored in some specimens and spermaceti- 

 white in others. In a lot of five perfect specimens, two were 

 white and three were wine-colored. 



Xassa scabriuscula Fowls. 



The apex of this species is in all respects like the last, except- 

 ing that the whorls are a trifle narrower, especially the initial 

 whorl, and they are white. Two specimens examined. 



JVassa miitalbilis Lamarck. (Fig. 38.) 



This nucleus differs from the preceding in having but one and 

 a-half whorls, which are more rounded, especially the first which 

 is knob-shaped and large. The color is spermaceti-white and the 

 whorls are shiny. The first three post-nuclear whorls are costate 

 after which they become smooth. Several specimens examined. 



Family COLUMBELLID^. 



Genus COL,UJ»f BEL,L,A Lamarck, 



Coluiu'bella mercatoria Linn6. (Figs. 39, 40.) 



Apex of good size, rounded, smooth, consisting of two whorls, 

 rapidly enlarging. The whorls are very flat, the first one particu- 

 larly so (fig. 40), and in a lateral view the first whorl shows 

 simply as a fiat cap. The nuclear whorls are perfectly smooth, 

 but the post-nuclear whorls are spirally lirate. In perfect speci- 

 mens the apex is deep purple in color, but in worn specimens it is 

 white, A number of specimens examined with no variation. 



Coluiu'bella fastigiata Sowerby. (Fig. 41.) 



Apex of good size, rounded, smooth, consisting of three and a- 

 half whorls regularly increasing in size. The first two whorls are 



