106 MOLLUSCA FROM THE CRAG. 



10. RissoA CRAssi-STRiATA. S. Wood. Tab. XI, fig. 13, a — b. 

 RissoA CRASsi-sTuiATA. S. Wood. Catalogue 1842. 



R. Testa turritd, elevatd, crassd; anfractibus b — 6, convexis ; longitudinaliter costatis ; 

 cosfis 10 — 12, rectis, obimis; transversim lineatis, lineis pmicis elevatis; suturisprofundis; 

 aperturd subrotii/idd ; labro exfus incraHsato, marpnato ; intus denticulato. 



Shell turriculate and elevated, thick and strong, with five or six convex volutions ; 

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

 costse ; transversely striated ; striae 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 It. sculpta, Phil, (En. Moll. Sic. vol. ii, p. 132, t. 23, f. 21), but it 

 appears to difi'er 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 striae 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. >S'. JFood. Tab. XI, fig. 12, a — b. 



RissOA COSTULATA. S. Wood. Catalogue 1842. 



R. Testd turritd, elongatd, perforata; anfractibus 5 — 6, convexiusculis super ne 

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

 striatis ; suturisprofundis; 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 strise, caiTied over the ribs ; aper- 

 ture ovate ; peristome disconnected ; outer lip sharp, denticulated within ; left lip 

 slightly reflected ; umbilicus small and open. 



Axis, I of an inch ; diameter, % 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, 



