94 FAUNA OF THE CORNBRASH. 



fine lines which decussate them." In the upper whorls there are about three spirals, 

 in the next five, and lastly seven. The cross lines are twice as numerous and 

 branch below. " The principal carina, which occurs about two thirds down, 

 carries the uinbilicated slit band. This occupies the most salient position in 

 each whorl." The spirals below this are more numerous and the cross lines 

 curve backwards above the slit and forward below it. " The base is tolerably 

 tumid, with strong spiral ornaments," and with cross lines twice as numerous as 

 they. " Aperture quadrate or trapezoidal. Columella thick and curving 

 forwards." The clearest specimen shows no umbilicus. 



Distribution. — Thirty-seven specimens have been seen, all from Scarborough, 

 but the records for Rushden and Peterborough districts have not been verified. 

 The species is widely spread in Russia, and is said by D'Orbigny to occur also in 

 the Oxfordian of Normandy and the Ardennes. 



Relations. — The species certainly resembles P. mnensteri, Romer {fi<l< } D'Orbigny), 

 but that has a fairly open umbilicus. Perhaps this should not carry much weight, 

 but we do not know the details of its ornamentation. Except for this detail of 

 ornament, it would also resemble P. filigrana from a similar horizon. It is 

 remarkable that after so long an interval in Pleurotom.aHa-growt'h as occurred 

 before the Cornbrash, the earliest to arrive should have originated apparently in 

 the north or east. 



Pleurotomaria debilis, sp. nov. Plate VIII, fig. 25. 



Type. — Length 32 mm., breadth 27 mm. Spiral angle 58°. Six whorls are 

 seen, but only parts retain the shell. The surface is not uniformly convex, but has 

 no keel, the slit band being at the level of greatest convexity. The posterior part 

 of each whorl shows three or more strong spirals, which rise and fall over strong 

 longitudinal risings, about thirty per whorl in number. The central part, where 

 preserved, shows several weaker spirals, with the slit band in the centre. The 

 anterior portion is thrown again into undulations half the size and twice the number 

 of the upper ones. The base is convex, rounding into the side. Probably it is 

 skinned, for the striae soon die away. The umbilicus is small. From Bedford. In 

 the Northampton Museum. 



Distribution. — There is a second specimen from the same locality which may 

 belong here, but the spirals are stronger and more continuous, and the base is 

 striated. 



Relations. — The nearest ally, with twice as many undulations below the slit 

 band as above, is PI. pagodus (Desk), from the Great Oolite of Normandy, but 

 the base is concave. If we neglect the detail of the number and position of the 

 undulations, this might come under the description of P. filigrana var. unci data 



