PLEUROTOMARIA. 397 



figure (also from a Dundry specimen) is characteristic, though the aperture is not 

 seen. The species does not appear to have been recognised by Deslongchamps in 

 the Normandy beds. On the other hand, Tawney regarded it as one of the 

 commonest species at Dundry. He suggested that PL Allionta, d'Orbigny, might be 

 a synonym. 



Description : 



Height . . . . .40 mm. 



Basal diameter . . . .33 mm. 



Spiral angle ..... 48°. 



Shell acutely conical, not umbilicate. Spire perfectly regular. Whorls 

 (ten to twelve) flat, with a close suture, and spiral lines of unequal strength ; these 

 are more or less granulated towards the posterior and anterior margins of each 

 whorl ; the almost invisible suture lies between the raised lines which carry the 

 strongest granulations. 



The sinus-band forms a salient belt on the sides of the whorls, and is situated 

 some distance below the centre ; it is full, round, and rather narrow, having in 

 the apical whorls a central spiral line crossed by growth-lines, but in the later whorls 

 the growth-lines alone are seen, and even these are often effaced. The body- whorl 

 is angular at the periphery ; the base has a flat marginal area, but is excavated 

 towards the centre; it is spirally striated with slight radial decussation. Aperture 

 subrhomboidal and extremely depressed. 



In the smaller shells the columellar notch is very characteristic (Fig. 2), and 

 even in the larger shells a modification of this feature may be detected. In very 

 large forms (? PL Allionta) the notch is effete. 



Relations and Distribution. — PL punctata is a well-defined species, somewhat 

 remotely related to the elongata-group. Excellent specimens have been obtained 

 from Dundry. Good specimens are also obtained from the MurcMsonse-zone of 

 Coker, and inferior ones from the same horizon at Bradford Abbas. The Goncavus- 

 bed at Bradford Abbas furnishes us with a number of beautiful specimens. The 

 above are all in the Lower Division. 



In the Humphriesianns-zone of North Dorset typical specimens may 

 occasionally be met with. There is a large specimen in my collection, said to 

 come from the Parkinsoni-zone, which may possibly represent PL Allionta, d'Orb. 

 In this case there is no trace of the columellar notch. 



