132 MOLLUSC A FROM THE CRAG. 



This shell was published in my Catalogue as a distinct species, in consequence 

 of its crenulated strise, in which character it was considered by several eminent 

 conchologists, as well as by myself, to be well marked. For this reason I have 

 retained its present name, as also from its having a large and open umbilicus, by 

 the possession of which it differs from the preceding species, which has it entirely 

 closed. I cannot, however, but feel doubtful of the correctness of its separation, 

 and that the possession of more specimens may probably unite the two. It some- 

 what resembles T. umbilicalus, Mont., in its large and open umbilicus at all ages, if 

 it be a distinct species ; but that shell is never crenulated like ours. In the young 

 state it is much depressed, with a large and open umbilicus, the size of which, in 

 the adult shell, depends upon the greater or less elevation of the spire, but it is 

 always open. The spiral lines of stria? are about ten in number, generally alter- 

 nating, one large and one small ; all are more or less crenulated, and the peculiar 

 depression in the umbilicus gives a tooth-like projection, or twisting, to the lower 

 part of the columella. The circular ridges upon the base, in some specimens, are 

 also strongly crenulated ; these crenulations are probably more prominent and 

 apparent in the fossil state than they would have been in the recent shell. 



16. Trochus tricariniferus. S. Wood. Tab. XIV, fig. 6, a — b. 

 Trochus tricariniferus. S. Wood. Catalogue 1842. 



Tr. Testa orbiculato-conoided, crassd ; apice acuto ; anfractibus quinque, crenulatis ; 

 cingulis tribus, elevatis, instructis ; suturis profundis ; aperturd subquadratd ; umbilico 

 parvo ; columella obsolete unidentatd. 



Shell orbiculato-conoidal, thick, and strong, with a slightly elevated spire and 

 acute apex ; suture deep ; whorls five, ornamented with three elevated obtuse 

 carina?, crenulated by elevated and reflected lines of growth ; aperture subtrape- 

 zoidal, with an obsolete tooth upon the columella. 



Axis, \ of an inch. 



Locality. Cor. Crag, Sutton. 



This shell, small specimens of which are not rare, somewhat resembles the 

 figure and description of Tr. Guttadauri, Phil. En. Moll. Sic. t. 11, f. 1, but our 

 shell has an umbilicus nearly closed, and the volutions are not rounded ; the 

 aperture is of a subquadrate form. Small specimens have the carinas sharp, but 

 in the older ones they become rounded and obtuse, and there is sometimes a small 

 intermediate thread. The base has about half a dozen elevated stria? or ridges, 

 and the lines of growth are elevated into fine reflected fimbria?, most conspicuous 

 in young shells and between the ridges. The upper keel is much elevated, leaving 

 a deep sulcus round" the top of the whorl. The outer lip is sharp, sloping 

 inwardly to the thick part of the shell. 



The imbricated lines of growth on some specimens are closed and numerous, on 

 others they are fewer in number and more distant. Whether M. Philippi's 

 description of " sulci foveolati " relates to the spaces between these imbrications 



