78 MOLLUSCA FROM THE GREAT OOLITE. 



nodos sitd; ultimo anfractu ad basim angulalo siibnodoso; basi subconcavd, concentrice 

 striatd, striis tenuibus, profundis ad umbilicum minimum nuttis; aperturd subpentagond. 



Shell trochiform, subturreted ; apex rather acute ; whorls step-like, narrowed beneath 

 the band, transversely and finely striated, coronated in the middle by a circle of nodules, 

 subundulated even to the suture ; the sinus is large and deep, the band of the sinus is flat, 

 densely striated longitudinally, and situated beneath the nodules ; the last whorl is 

 angulated at lower margin and slightly nodulated; the base is somewhat concave, con- 

 centrically and very delicately striated; the umbilicus is very small or obsolete; the aperture 

 is nearly pentagonal. 



Locality. Two specimens only have been found in the Minchinhampton district. Both 

 are small compared with the fine specimen figured by M. Deslongchamps, who is very 

 fortunate in that respect, considering that the species is likewise very rare in Normandy. 

 Its position is the soft shelly Oolite beneath the planking at Minchinhampton Common. 



PLECROTOMARIA DISCOIDEA. Plate X, fig. 12. 



P. Testa turbinato-depressd, spirdobtusd, anfractibus subconvexis, lavibus et angustatis ; 

 sinu anffustissimo ; fascia sinus strictd, et planatd interdum vix notatd, infra medium an- 

 fractuum sitd; ultimo anfractu ad basim angulato convexo, basi subconvexd, laevi ,- umbilico 

 minuto out nullo, aperturd subquadratd. 



Shell turbinated, depressed: spire obtuse; whorls somewhat convex, smooth, and 

 narrow ; sinus very narrow ; the band of the sinus narrow, flattened, and smooth, some- 

 times scarcely distinguishable, and placed beneath the middle of the whorls ; the last whorl 

 is angulated, and convex at the margin ; the base is slightly convex, and smooth ; the 

 umbilicus minute or wanting ; the aperture subquadrate. 



The small elevation of the spire, which is only equal to two fifths of the basal diameter, 

 necessarily renders the whorls narrow ; the basal angle of the last whorl is unusually acute ; 

 the sutures of the whorls are strongly marked. 



Though possessing few distinctive characters, it is little liable to be confounded with 

 others ; the extreme smoothness, depressed form, and proximity of the sinus and fascia to 

 the base of the whorls, are obvious and sufficient features. Height 4 lines, basal diameter 

 10 lines. 



Locality. We can enumerate seven specimens ; they occurred in the white stone at 

 Bussage ; also in the lower portion of the formation on the south side of Minchinhampton 

 Common, where the rock is not very shelly. 



