PLEUROTOxMARlA. 429 



accept this view, and I am inclined to agree with him. Certainly one could fill a 

 plate with forms of the Ornatge which might possibly be regarded as intermediate 

 between PI. tuberculosa, Defrance, and PI. ornata, Sow. But under any 

 circumstances the fossils we are now considering differ so widely from the average 

 form of Sowerby's species as to merit distinction. Since a name is required, that 

 of "tuberculosa" is certainly appropriate. The type was obtained from "near 

 Caen in the Oolite bed." 



Description : 



Height . . . . .25 mm. 



Basal diameter . . . .55 mm. 



Spiral angle .... 128°. 



Shell turbinate, much depressed, widely umbilicate. The spire, though low, is 

 regular. Whorls (six) angular, and increasing by wide steps with a canaliculate 

 suture. The angle of each whorl is ornamented with very thick tubercles, and the 

 entire shell is pervaded by fine spiral lines, radially decussated in the earlier 

 whorls, and undulating towards the anterior margin of the later ones. 



The sinuS'band is rather wide, flat and submedian ; its ornaments vary with 

 the ornaments of the whorls, but anteriorly have a tendency to disappear, showing 

 only sinuous growth-lines. The body-whorl is relatively very large, euomphaloid, 

 and bicarinate ; the upper keel is grossly nodular ; in the lower keel the nodules 

 are drawn out spirally, exhibiting a dentate periphery. Base round, with a large 

 infundibuliform umbilicus. Aperture oval, depressed. 



Relations and Distribution. — This is pretty near to PI. ornata, var. sulcifera, 

 Deslongch. The form is rare in England. The best specimens come from Louse 

 Hill (Humjihriesianus-zone). The fossil quoted by Morris as from the " I. 0. 

 Bridport " came most probably from Burton Bradstock, whence also I have seen 

 specimens of PI. tuberculosa. 



371. Pleurotomakia oenata, Sowerby, 1818. Plate XXXVII, figs. 3 a, 3 b, 3 c. 



1818. Trochus ornatus, Soiverby. Min. Conch., pi. ccxxi, fig. 1. 

 Syn. 1823. — Pallium, Farey. Sowerby, Min. Conch., vol. iv, Index (Corri- 



genda). 

 1843. Pleurotomaria Pallium, Soiverby. Morris, Cat., p. 158 (edition of 1854, 



p. 271). 

 1873. — Morris. Tawney, Dundry Gasteropoda, p. 49 



(41). 



Bibliography, §c. — So long as this species was referred to the genus Trochus, 

 the name selected by Sowerby was open to Farey's correction. Subsequently 



