138 MOLLUSC A FROM THE CRAG. 



A very abundant shell. It differs from the preceding, A. striates, in being quite 

 free from strias on the upper part, and in having three keels at unequal distances 

 upon the volution, of which the lower one is the most prominent and permanent, 

 and the upper one, even the upper two, are sometimes evanescent. A small 

 incipient sinus is visible at the upper part of the aperture, which gives a depression 

 round the volution near, but not at, the suture, which character I do not observe 

 in the other species. This may possibly be the Skenea divisa, Flem. (Brit. An. 

 p. 314), Turbo divisa, Adams ; but these authors make no mention of the keel-like 

 ridges that surround the shell. 



Three or four coarse stria? or ridges cover the volution at the umbilicus, and the 

 lines of growth are elevated at that part, and are corrugated. The most abundant 

 variety is that which is entirely smooth above, with only one keel upon the base or 

 outer edge of the volution. 



3. Adeorbis tricarinatus. S. Wood. Tab. XV, fig. 6. 



Adeorbis tricarinatus. S. Wood. Catalogue 1842. 



A. Testa minutd, depressd, subdiscoided ; anfractibus subcylindraceis ; cinyulis tribus 

 acutis, subequidistantibus, instructis ; interstitiis spiraliter striatis ; superne et in/erne 

 planiusculis, umbilico magno. 



Shell small, depressed, subdiscoidal ; with three convex or rather subcylindrical 

 volutions, furnished with three sharp subequidistant and elevated carinas spirally 

 striated between them ; shell rather flat above and beneath, with a large open 

 umbilicus, slightly corrugated by lines of growth. 



Diameter, \ of an inch ; altitude, \ its diameter. 



Locality. Cor. Crag, Sutton. 



I have about half a dozen specimens in my cabinet with the above characters, 

 in which they appear to differ from the two preceding species sufficiently to be 

 considered specifically distinct. 



A. supra-nitida possesses the keels, but less prominently, and less equally dis- 

 tributed, and it is perfectly smooth except in the umbilicus. A. striatus possesses 

 the striae, but has no vestige of carinas ; and this shell has not the coarse spiral 

 strias of the umbilicus. It is possible that they may be only varied forms of one 

 species, but the numerous specimens in my cabinet appear to preserve the above 

 distinctions, and they must for the present, therefore, remain separate. 



