MONOGRAPHS OF THE GENERA 

 CYCLOSTREMA, ADEORBIS, and TEINOSTOMA. 



By Akthue Adams, R.N., E.L.S., etc. 



Genus CYCLOSTREMA, Marryatt. 



Shell orbicular depressed, widely umbilicated ; spire small j 

 whorls rounded, spirally ridged, radiately ribbed or cancellated. 

 Aperture not pearly within, orbicular; peritreme continuous, 

 acute. 



This genus with its allies, which we have here, for the sake of 

 convenience, considered in the light of subgenera, together with 

 the genus Adeorbis, appear to constitute a peculiar group of Tro- 

 cJiuls, the shells of which may at once be distinguished by the 

 absence of pearly nacre in the interior of their apertures. The 

 genus Viirrnella, of C. B. Adams, seems more nearly related to 

 the Scissurella race than to Adeorbis. 



1. cancellata (pi. 255, f. 5, 6), Marryatt. — Testa alba, lineis 

 longitudinalibus et transveisis elevatis decussantibus inde cancel- 

 lata ; apertura labiis cancellatis ; cancellis transversim striatis. 

 Obs. This beautiful shell, procured by Captain Marryatt from 

 West Indies, and made the type of a peculiar genus at the sug- 

 gestion of Dr. Leach, differs from the other species of the genus 

 in being plicate above and below a peripheral keel ; the specific 

 name is hardly characteristic. We have reproduced the original 

 description. 



2. l.evis (pi. 255, f. 3, 4), Kien. — Testa orbicularis, nivea ; 

 spirii depressa ; aufractibus transversim costellatis ; costellis re- 

 gularibus, superis, distantioribus ; interstitiis leviter concavis ; su- 

 tu r is profundis subcanaliculatis ; labro simplici ; umbilico per- 

 amplo. Obs. The Cyclostrema dialretum, Gould, is the same as 

 this species, which has been considered by Reeve as the Turbo 



vol. in. 2 t 



