GASTEROPODA. 41 



I have given the name assimilis from its close similarity, in all other respects than size, 

 to the large Bridlington shell robusta. The uniformity in size between the Crag specimen 

 and the two Middle Glacial ones, renders it probable that the specimen figured is full 

 grown ; I have, therefore, considered this species as distinct from robusta, and assigned 

 to it a separate name. It is, however, possible that, as some existing shells assume 

 gigantic proportions under certain arctic conditions, the shell thus appearing in the Red 

 Crag before the Glacial conditions had actually fallen upon Britain, and occurring in 

 similar size in the Middle Glacial Sand by virtue of those causes, whatever they may be } 

 to which the presence of so many southern species in these sands is due, became inflated 

 by the truly arctic conditions under which the Bridlington shells lived, to the gigantic 

 dimensions possessed by the species I have figured under the name of robusta. The shell 

 differs from Trevelyana in the greater length of the body whorl relatively to the spire, 

 and in having a less prominence of shoulder: also in its greater size. 



Pleurotoma hystrix, Jan. Supplement, Tab. VI, fig. 3, a, b. 



Pleurotoma histrix, Jan. Catal., p. 10, No. 59, 1832, fide Bellardi. 

 Rhaphitoma histrix, Bellardi. Mon. delle Pleur. Foss., p. 85, t. iv, fig. 14, 1847. 

 Defrancia histrix, A. Bell. Ann. and Mag. Nat. Hist., September, 1870. 



Spec. Char. " Testa subfusiformi, elongatd, angusta, costis longitudinalibus et trans- 

 versalibus exilissimis, lau/ellosis clathrata ; in earum intersecatione papillis acutis, erectis 

 hirsuta ; anfractibus planiusculis, elongatis, postice lavibus ; spira elata, apertura ovato- 

 elongata ; labro intus sulcato ; canali longinsculo." — Bellardi. 



Length, yfths of an inch. 



Localities. Cor. Crag, Sutton {Bell). Red Crag, Walton-on-the-Naze. 



The specimen figured was obtained by myself from Walton, from which place another 

 has since been obtained by Mr. Bell. It much resembles Fusus cancellatus, J. Sow., 

 Clavatula cancellata, 'Crag Moll.,' but the present shell is more elongated, and there is a 

 broad sinus adjoining the suture ; this leaves a blank or naked depressed space at the top 

 of the volution, or at least shows only lines of growth of the sinuated aperture. The 

 shell is elegantly cancellated, and the outer lip is somewhat thickened and denticulated on 

 the inside. This is not Murex hystrix, Linn. Mr. Bell gives the species as from the Cor. 

 Crag. ('Ann. and Mag. Nat. Hist.,' May, 1871), but I have not seen the specimen. 



Pleurotoma tenui striata, A. Bell. Crag Moll., vol. i, p. 62, Tab. VII, fig. 12 (as 



Clavatula lavigata). 



Pleurotoma tenuistriata, A. Bell Ann. and Mag. Nat. Hist, for May, 1871. 



Locality. As in ' Crag Moll.' 

 6 



