134 MOLLUSCA FROM THE CRAG. 



are on the upper half of the volution, and the same number are on the base, with 

 only three between the keels ; those upon the base are most prominent and distinct, 



In Savigny's great work upon Egypt is the representation of a shell somewhat 

 resembling this species, but which, from the figure, appears to be too strongly 

 imbricated, and to have the aperture too circular, to be considered identical ; a 

 comparison with the shell itself is necessary for such determination. 



Many of the shells in this genus also have the exterior much altered by 

 decortication, and the determination of some of the' species is not by any means 

 satisfactory. 



Margarita,* Leach, MS. 1819. 



Trochus (spec.) Linn. 



SOLABIELLA, S. U'ood. 1842. 



Gen. Char. Shell thin, subconical, trochiform ; spire moderately elevated ; volu- 

 tions few, rather inflated ; striated, sometimes costated ; aperture subcircular ; 

 peritreme sharp, discontinuous, interrupted by the previous volution ; umbilicus 

 generally large and deep ; operculum corneous, multispiral. 



The animal of this genus much resembles that of Trochus, and it is considered 

 by some conchologists as not deserving of generic distinction. There is, however, 

 a delicacy and generally a semitransparency in these shells, accompanied by a large 

 and open umbilicus in all the species, that at least entitles them to a sectional sepa- 

 ration, and as the name was employed in my Catalogue, I have retained it here. 



Mr. G-. B. Sowerby, sen., has described fifteen recent species of this genus in 

 the ' Malacological Magazine,' 1838, all of which are northern forms. 



1. Margarita elegantissima. Bean, MS. Tab. XV, fig. 1. 



M. Testa orbicularis conoided, tenni ; apice acuto ; anfractibus quinque, superne 

 convexis, inferne planulatis ; longitudinaliter oblique costulatis ; interstiliis tenuissime 

 strialis ; umbilico magno, bicarinato. 



Shell orbiculato-conoidal, thin, and fragile, with a slightly elevated spire and 

 acute apex ; volutions five, convex above, rather flat beneath, outer edge obtusely 

 angular ; longitudinally costated, with elevated, reflected, or imbricated costas, 

 finely striated transversely ; umbilicus large, bicarinated. 



Axis, J of an inch. 



Locality. Mam. Crag, Bridlington. 



The cabinet of Mr. Bean, of Scarborough, has furnished me with the only 

 specimen of this species that I have seen. It appears to be distinct from any 

 with which I am acquainted, and I have, in accordance with that gentleman's 

 opinion, considered it a new species. The characters which most distinguish it 



* Etym. Margarita, a pearl; from the nacreous character of these shells. 



