GASTEROPODA. 101 



costse 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, -|- 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 speci- 

 mens 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, 184.3. 



Cyclostrema Zetlandica. Thorpe. Brit. Mar. Conch, p. 158, 1844. 



li. Testa crassd, ovato-conoided ; anfractibus 5 — 6, convexis, tumidis ; (singulis trans- 

 versis, elevatis, et grandis, circa quinque, longitudinal iter costatis, decussantibus, alveolatis , 

 apertura rotundo-ovatd ; labro intus lavigato ; ultimo (infract u cingulum ad umbilicum 

 ferente. 



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

 covered with four or five large elevated strise 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, -^q 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 costas 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. 



