GASTEROPODA. 101 



costae obsolete upon the lower portion ; aperture ovate, rather narrow or angulated 

 at the upper part ; peristome continuous, with a slightly thickened outer lip, oblique 

 and projecting ; umbilicus covered ; suture deep and distinct. 



Axis, I of an inch. 



Locality. Cor. Crag, Sutton. Recent, British Seas. 



Not a very abundant species. From a careful comparison with the well-known 

 recent species I have no doubt of its identity. The last whorl is slightly contracted, 

 or rather depressed, and thrown a little out of its regular descending volution, giving 

 the lower half of the shell a cylindrical form ; the base of the inner lip is slightly 

 reflected, like that in the genus Scalaria, and covers the umbilicus. In some specimens 

 the ribs may be seen over the whole whorl, but in general only so at the upper half 

 of it. 



2. RISSOA ZETLANDICA. Mont. Tab. XI, fig. 7, a b. 



TURBO ZETLANDICA. Mont. Linn. Trans, xi, p. 194, t. 13, fig. 3. 

 CYCLOSTREMA ZETLANDICA. Flem. Brit. An. p. 312, 1827. 

 RISSOA ZETLANDICA. S. Wood. Catalogue 1842. 



Morris. Catal. of Brit. Foss. p. 161, 1843. 

 CYCLOSTREMA ZETLANDICA. Thorpe. Brit. Mar. Conch, p. 158, 1844. 



R. Testa crassd, ovato-conoided ; anfractibus 5 6, convexis, tumidis -, cingulis trans- 

 versis, elevatis, et grandis, circa quinque, longitudinaliter costatis, decussantibus, alveolatis ; 

 apertura rutundo-ovatd ; labro intus laevigato ; ultimo anfractu cingulum ad umbilicum 

 ferente. 



Shell strong, ovato-conical ; apex rather obtuse, with five convex volutions, covered 

 with four or five large elevated stria? or ridges, which are decussated by longitudinal 

 ribs ; aperture subcircular ; inside of outer lip without denticulations, and furnished 

 with a thick or double ridge at the umbilicus. 



Axis, & of an inch. 



Locality. Cor. Crag, Sutton. Recent, Zetland. 



Not a very abundant species. It appears to be identical with the shell from the 

 North Seas. The spiral ridges are at regular distances, excepting those below the 

 volution, where, after a wider space, there are two ridges, or rather a double ridge, 

 which covers the immediate portion of the base around the umbilicus. On the upper 

 part of the whorl there is a slight depression, giving a small shoulder to the volution. 

 The longitudinal costae are carried over the base, though they are less elevated there 

 than upon the body of the shell ; and the transverse ridges are more prominent than 

 the longitudinal ones, which are tuberculated at the point of decussation. The thick 

 or double ridge gives a crenulated groove at the base, and it is this character which 

 best distinguishes the species. 



