106 SUPPLEMENT TO GREAT OOLITE MOLLUSCA. 



perpendicular equal lines, forming a delicately cancellated surface ; the last volution has 

 the base wide, somewhat convex, with regular concentric and radiating lines, the latter 

 being the less conspicuous ; there is scarcely any umbilical depression ; the sinus is large, 

 placed in the middle of the volutions ; the fascia of the sinus is delicately cancellated ; the 

 nodose elevations upon the upper half of each volution are regular, numerous, and not 

 very strongly defined in the greater number of the specimens. 



The height is equal to two thirds of the basal diameter. Of the seven specimens 

 examined, the largest has a basal diameter of about an inch. 



Geological Posiiion and Locality. The Forest Marble of Burton Bradstock ; in the 

 collection of W. Walton, Esq. 



Pleurotomaria recondita, Li/c. Tab. XLV, fig. 7. 



Testa trochiformi, discoidea, anfractibus (4) suhplanis, inferne obtuse carinatis ; fascia 

 sinus lata, transverse delicate striata, in medio anfractam situ ; anfractibus cinyilUs anxjustis 

 (3 — 4) supra et infra sinus instructo, striis obliquis tenuissimis, inipressis ; carina mar- 

 gincdi lavi ; basi laio, concavo, umbilicato, delicate concentrice striato. 



Shell trochiforra, discoidal ; volutions (4) flattened, but rendered concave in the lower 

 portions by a prominent, obtuse, smooth, marginal carina ; the fascia of the sinus is 

 mesial, wide, with very delicate transverse striations ; above aud beneath the sinus are 

 three or four narrow encircling little costae, which are impressed by delicate oblique stria- 

 tions ; the base is wide, concave, with a distinct umbilicus, with fine concentrie striations ; 

 the outer lip and sinus have not been obtained perfect. 



The height is equal to about three fifths of the basal diameter. 



A small species, remarkable for the great breadth of the mesial band, and the pro- 

 minence of the infero-raarginal smooth carina. 



Gcoloc/ical Position and Locality/. The Great Oolite of Bussage, near Bisley Common, 

 and of Minchinhampton Common ; it is rare. 



AcTEONiNA Ll'idii, p. 27. Tab. XXXI, fig. 16, and Tab. XLI, fig. 18. 



A fine series of examples kindly communicated by INIr. Walton, and collected by him 

 in the Forest Marble of Laycock, has enabled the artist to illustrate the more striking 

 varieties of figure. The differences in the elevation of the spire are so considerable that 

 any measurement of the spiral angle is useless ; the sides of the volutions are always 

 flattened, with a mesial angle ; in short spired examples the space anterior to the angle is 

 nearly concealed, and the space posterior to it is nearly horizontal. 



Another remarkable instance of variability in the elevation of the spire in the same 



