1 94 MARGINELLID.E 



Genus PACllYBATHRON, Gaskoin. 



Shell subcylindrical, striated longitudinally; spire flat, 

 volutions perceptible ; aperture narrow, channelled pos- 

 teriorly; columella with strong, distant denticulations at 

 the fore part; inner lip with a broad, thick, flat callus 

 extending the entire length of the shell, transversely 

 strongly grooved; outer lip thick, denticulate internally. 



Ex. P. cassidiforme, Gaskoin, pi. 20, fig. 4. 



The curious little shells forming this genus most re- 

 semble species of Persiciila, but the callus of the inner 

 lip is very much developed and furnished with strong 

 transverse grooves. 



Species of Pachybathron. 

 cassidiforme, Ga.^k. marginelloideum, Gask. 



Genus VOLVARIA, Lamarck. 



Shell subcylindrical, semipelliicid; spire short, obso- 

 lete; aperture narrow, anteriorly dilated; columella si- 

 nuous in front, subflexuous, obliquely truncated, and with 

 four oblique plaits; outer lip slightly thickened, but with- 

 out a marginal varix. 



Syn. Hyalina, Schmn., not Gray. Volvarius, Montf. 



Ex. V. triticea, Lamarck, pi. 20, fig. 5. Shell, V. 

 pellucida, Schumacher, fig. 5, a. 



The Volvaria of Lamarck appears to be restricted to 

 one recent species, having the spire short and the outer 

 lip only slightly thickened; the sub-genus Volvarina, 

 however, is numerous in species. 



