132 MOLLUSCA FROM THE CRAG. 



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

 its crenulated striae, in which character it was considered by several eminent con- 

 chologists, 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 somewhat resembles T. umbilicatus, 

 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 

 o-reater or less elevation of the spire, but it is always open. The spiral lines of striae 

 are about ten in number, generally alternating, 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. JFoocl Tab. XIV, fig. 6, a — d. 

 Tkochus tricarinifekus. S. Wood. Catalogue 1842. 



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

 cingulis tribus, elevatis, instructis ; suturis profundis; aperturd subquadrafd ; umhiUco 

 parvo ; cohmelld 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 carinas, 

 crenulated by elevated and reflected hues of growth ; aperture subtrapezoidal, 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 sub- 

 quadrate form. Small specimens have the carinae 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 striae or lidges, and the lines of gro-wth are elevated 

 into fine reflected fimbriae, 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 close 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 I cannot say. There 



