ADEORBIS. 255 



late at the periphery. Aperture not pearly within, transversely 

 ovate; inner lip sinuated ; peritreme interrupted; outer lip 

 arcuate, simple, acute. Obs. The principal difference between 

 this genus and Cyclostrema consists in the more or less trochi- 

 form appearance of the shell, in the whorls being either smooth 

 or spirally striated, and especially in the peritreme not being cir- 

 cular and continuous. 



1. subcarinata (pi. 256, f. 7), Montag. — Testa suborbicu- 

 laris, depressa, late umbilicata ; anfractu ultimo ad peripheriam 

 subcarinato, liris quatuor spiralibus ornato ; apertura rotundato- 

 ovata; labio subreflexo, labro acuto. Obs. This somewhat rare 

 British species is the type of the genus ; the animal, however, 

 does not appear to have been hitherto studied. 



2. plana (pi. 256, f. 3, 4), A. Ad. — Testa orbicularis, dorso 

 plano-convexa ; spira depressa, ; anfractibus plain's, supra transver- 

 sim striatis, infra lajvibus ; apertura subcirculari, supra angulata ; 

 uinbilico peramplo, anfractibus intus conspicuis. Obs. A large 

 (for the genus) species, with a very flat spire and with the whorls 

 concentrically finely striated. 



3. elegans (pi. 256, f. 1, 2), A. Ad. — Testa orbicularis, dis- 

 coidea, tenuis, semipellucida; spira depressa; anfractibus rotun- 

 datis, transversim omnino striatis ; suturis distinctis ; apertura 

 subcirculari, supra angulata ; umbilico peramplo. Obs. A beau- 

 tiful semipellucid species, remarkable for the extreme elegance of 

 its form ; the aperture is peculiarly angulated at the fore part. 



4. planorbcla (pi. 256, f. 5, 6), A. Ad. — Testa orbicularis, 

 planorbula ; spira depressa ; anfractibus lrevibus, rotundatis ; su- 

 turis distinctis ; apertura subcirculari, supra angulata ; umbilico 

 permagno, patulo. Obs. The aperture in this cyclotiform species 

 is circular and somewhat dilated, yet the sum of all the characters 

 shows it to belong more properly to Adeorbis than to any other 

 genus. 



5. nitida (pi. 256, f. 9, 10), A. Ad. — Testa orbicularis, kevis, 

 tenuis, nitida ; spir& elatiuscula ; anfractibus prope suturam sub- 

 angulatis; suturis profundis, subcanaliculatis ; apertura subcir- 

 culari, supra angulata ; umbilico magno, peromphalo angulato, 

 acuto. Obs. The principal peculiarity of this species is the an- 

 gular keel round the umbilicus ; the whorls and aperture are 

 more rounded than usual and the surface of the shell is polished. 

 It may possibly belong to the genus Cilhna, A. Ad. 



6. Adamsii (pi. 256, f. 8), Fiscli. — Testa translucida, corneo- 



