28.2 Mr. H. Seeley on Cambridge Palceontology : — 



length of the shelly composed of four whorls, which rapidly 

 increase in size, and are rounded, inflated, and striated. Body- 

 whorl very large, ornamented on its most tumid part with two 

 keels, which, as they approach the aperture, become more 

 elevated ; the lower one then diverges rapidly anteriorly, and 

 the upper one is turned a little towards the spire : a part of 

 the cast of the last whorl is directed up the spire, and appears 

 to have been produced into a canal ; so that the shell was pro- 

 bably digitated like P. Fittoni (Forbes). Between the keels 

 are four strise, of which the outer ones are least elevated. 

 Posterior to the keels the casts show but two strife, and those 

 near to the rib. Anteriorly the strise were more numerous ; 

 but, from the canal being always broken, the number is not 

 evident : there appear to have been five, with two beyond them 

 less distinct. Mouth crescentic, oblique. Height -^-^ inch, 

 width y'^g inch. 



This small species approaches most closely to P. marginatum 

 (l)'Orb.), but is distinguished by the more elevated spire, som.e- 

 what different ornamentation, and small size. 



Not uncommon*. Cambridge and Ashwell. Coll. Univer- 

 sity ; J. Carter, Esq. ; Mr. W. Farren. 



The figure of Pyrula Smithii, in Trans. Geol. Soc. 2 ser. vol. iv. 

 t. 11. fig. 15 a, may possibly belong to this species. 



Pterodonta marginata. PI. XI. fig. 2. 



Shell elongated, finely striated. Whorls elevated, nearly two- 

 thirds as high as wide, somewhat inflated and round; each 

 ornamented round the middle with about a dozen prominent 

 tubercles. The body-whorl is small, and has on its upper part 

 a prominent angle, above which is a space flat and oblique, 

 and more than half the width of the whorl above. The space 

 below has indications of a keel, which, however, is very faint, 

 and becomes quite obsolete on the last fourth of the whorl, 

 which is flat. The last whorl is gradually heightened towards 

 its mouth, up to the middle of the whorl above. The tooth 

 is placed immediately below the keel (and, in my specimen, 

 at the edge of the mouth) ; it is large, elevated, and round, 

 and reduces the mouth to a narrow elongated slit widened at 

 the top, as in Pteroceras. The columellar lip, too, as in that 

 genus, is enormously thickened. 



This species is most nearly related to P. carinella (P. & R.), 

 but difi'ers in the tuberculated whorls, small body-whorl, &c. 

 But it much more closely resembles Rostellaria marginata (Sow.), 

 so closely that, where the mouth is wanting, it will be difficult 



* These remarks refer iu all cases to relative, not actual, rarity. 



