106 MOLLUSCA FROM THE CRAG. 



10. Rissoa ckassi-striata. S. Wood. Tab. XI, fig. 13, a — b. 



Rissoa crassi-stkiata. S. Wood. Catalogue 1842. 



B. Testa turritd, elevatd, crassd ; anfractibus 5 — 6, convexis ; longitudinaliter costatis ; 

 costis 10 — 12, rectis, obtusis ; transversim lineatis, lineis paucis elevatis ; suturis 

 profundi?; aperturd subrotundd ; labro extus incrassato, marginato ; intus denticulate. 



Shell turriculate and elevated, thick and strong, with five or six convex volu- 

 tions ; a deep and distinct suture, externally ornamented with 10 — 12 vertical and 

 obtuse costa3 ; transversely striated ; strise or ridges few and elevated, carried 

 over the ribs ; aperture subcircular, with a thickened and marginated outer lip, 

 denticulated within the mouth. 



Axis, \ of an inch ; diameter, nearly \ of the axis. 



Locality. Cor. Crag, Sutton. 



This is also an abundant species, and I have found it only at one locality. It 

 somewhat resembles B. sculpta, Phil. (En. Moll. Sic, vol. ii, p. 132, t. 23, f. 21), 

 but it appears to differ in several characters : the costse are more prominent than 

 those represented at the above reference ; it has also a thicker and more prominent 

 varix upon the outer lip, in the adult state, a deeper and more distinct umbilicus, 

 and it has six or eight denticulations within the outer lip, with the volutions more 

 convex. In perfect specimens the strise are coarse and elevated, about six or eight 

 in the last volution ; and these are continued over the ribs, which are seldom more 

 than ten in number. Many specimens have the costse worn smooth, much 

 resembling B. obscura of the same author (t. 23, f. 10). 



11. Rissoa costulata. 8. Wood. Tab. XI, fig. 12, a — b. 



Rissoa costulata. S. Wood. Catalogue 1S42. 



B. Testa turritd, elongatd, perforata; anfractibus 5 — 6, convexiusculis superne 

 subangulatis ; longitudinaliter costulatis ; costulis numerosis, confertis, rectis ; transversim 

 striatis ; suturis profundis ; aperturd ovatd; labro simplici, intus denticulato ; umbilico 

 parvo. 



Shell elongate, turreted, and slender, with 5 — 6 slightly convex volutions, sub- 

 angulated at the upper part, with a deep, well-defined suture ; costuLse numerous, 

 20 — 25, and erect, crossed by transverse impressed striae, carried over the ribs ; 

 aperture ovate; peristome disconnected; outer lip sharp, denticulated within; 

 left lip slightly reflected ; umbilicus small and open. 



Axis, y of an inch ; diameter, -f of the axis. 



Locality. Cor. Crag, Sutton. 



This shell is not very abundant ; I have a few specimens which are sufficiently 

 perfect to exhibit well-marked characters. It somewhat resembles T. decussatus, 



