136 MOLLUSCA FROM THE CRAG. 



3. Margarita trochoidea. S. Wood. Tab. XV, fig. 2. 



Margaeita trochoidea. S. Wood. Catalogue 1842. 



M. Testa orbiculato-trochided, depressd, tenui, fragili ; apice obtusiusculo, aiifractibas 

 quatuor, convexis, superne depressis apud suturas, ad basim obtuse angulatis, subtus 

 rotundatis ; transversim tenuissime striatis ; aperturd suborbiculari ; umbilico mayin) 

 pro/undo. 



Shell depressedly conical, trochiform, thin, and fragile ; volutions four, convex above, 

 slightly flattened near the suture, convex or rounded beneath, with an obtuse angle at 

 the outer edge ; covered with fine transverse or spiral strife ; aperture subcircular, 

 impressed by the body whorl with a sharp expanded and curved outer lip ; umbihcus 

 large and deep. 



Awis, \ of an inch ; diameter |. 



Locality. Cor. Crag, Sutton. 



Fragments and small specimens of this species are abundant. The diameter of the 

 base of the specimen figured does not exceed thi'ee eighths of an inch, although frag- 

 ments indicate at least half an inch. The volutions are convex both above and 

 beneath the subcarinated edge, and the umbilicus is visible to the spire, characters that 

 distinguish this species from any other with which I am acquainted. 



Adeorbis,* S. Wood. 1842. 

 Helix (spec.) Mont. 

 Trochus (spec.) Brown, Nyst. 

 Cingula (spec.) Flem. 

 Natica (spec.) Phil. 

 Valvata (spec.) Phil. 

 Delphinula (spec.) Bast. 

 Margarita (spec.) S. Wood. 



Gen. Char. Shell generally small, suborbicular, depressed, with a few nearly dis- 

 coidal and rapidly increasing volutions, umbilicus large and deep ; peritreme entire, 

 and nearly continuous, slightly interrupted by the previous volution, deeply sinuated 

 on the inner side, and having a minute or incipient sinus at the upper part of the 

 aperture, near the junction of the body whorl. 



As there was not any genus established at the time I compiled my Catalogue in 

 which 1 could place some small shells from the Crag, possessing the above characters, 

 the above name was proposed for their reception. Conceiving that an animal with 



* Etyni. Adeo, to approach, orhis, a circle. 



