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 Position and Locality. The Forest Marble of Burton Bradstock ; in the 
collection of W. Walton, Esq. 
PLevRoTOMARIA REcONDITA, Lye. ‘Tab. XLV, fig. 7. 
Testa trochiformi, discoidea, anfractibus (4) subplanis, inferne obtuse carinatis ; fascia 
sinus lata, transverse delicate striata, in medio anfractum situ ; anfractibus cingillis angustis 
(83—4) supra et infra sinus instructo, striis obliquis tenuissimis, impressis ; carina mar 
ginali levi; bast lato, concavo, umbilicato, delicate concentrice striato. 
Shell trochiform, 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-marginal smooth carina. 
Geological Position and Locality. 'The Great Oolite of Bussage, near Bisley Common, 
and of Minchinhampton Common ; it is rare. 
Acrronina Lutwu, p. 27. Tab. XXXI, fig. 16, and Tab. XLI, fig. 18. 
A fine series of examples kindly communicated by Mr. 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 
