7 '22 MR. E. W. HARMER ON THE CRAG OE ESSEX. 



P 



Tov. 1900, 



Ovula spelta. 





Mytilus hesperianus. 







Cyprcsa avellana. 





Nucula IcBvigata. 







Columbella sulcata. 





Cardium Parkinsoni. 







* Cassidaria bicatenata. 





decorticatum. 







Nassa labiosa. 





Astarte obliquata. 







elegans. 





Galeotii. 







^Purpura tetragona. 





Basterotii. 







Trophon costifer. 





* Omalii. 







muricatus. 





* Burtinii. 







elegans. 





Woodia digitaria. 







Pleurotoma Bertrandi. 





Cyprina rustica. 







Vermetus intortus. 





Gastrana laminosa. 







Troches sidjexcavatus. 





Venus imbricata. 







cineroides. 





*Cytherearudis. 







Dentalium dentalis. 





Corbulomya complanata. 





The names of those marked 



with an asterisk may be found 



in 



old lists of 



Norwich Crag shells, but no trace of them has been discovered in 



latt 



) years, and 



I doubt whether the references are reliable. 







In addition to these, some others, which had survived up to the 

 Butleyan Period, and are all more or less characteristic of the Butley 

 zone, are exceedingly rare in the Icenian Beds, namely : — 



Nassa reticosa. 



granulata. 



propinqua. 



Neptunea contraria. 

 Pleurotoma mitrula. 

 Natica hemiclausa. 

 catenoides. 



Natica mittepunctata. 

 Cardita corbis. 



scalaris. 



senilis. 



Cdrdiu m intcrruptum. 

 Mactra arcuata. 



Among the northern species recorded from the Norwich Crag which 

 are unknown in the Red Crag may be mentioned Trophon Gunneri, 

 Tr. bemiciensis, Velutina undata, Margarita groenlandica, Rhyn- 

 clionAla psittacea, 1 Leda pernula, Astarte elliptica, and A. borealis, 

 only the last-named, however, being abundant. While Neptunea 

 contraria is very rare in this zone, iV. antiqua (dextral) is one of 

 its common shells. 



The comparatively modern, as well as more boreal, character of 

 the Icenian Crag is further shown by its meagre fauna of not 

 more than 150 species in all : many of them being excessively 

 rare, and most of the more abundant of them typical British forms. 2 

 Not more than about 40 are really common, and of such only 5 or 

 6 are not known living, the latter being characteristic of the higher 

 rather than of the lower zones of the Crag ; 2 only are southern, 

 and 9 northern. It* the list of marine mollusca (70 in all) obtained 

 by Mr. James Beeve from one of the richest of the Icenian localities 

 (Bramerton, near Norwich), 3 the result of many years' work, be 

 compared with those from the Bed Crag of Little Oakley or Butley, 

 the distinction between the Bed and Norwich Crags will be, I think, 

 apparent. 



1 Mr. Alfred Bell is said to have found this species at one locality in the 

 Red Crag. 



2 The molluscan fauna of southern seas contains a greater number of species 

 than that of those to the north, that of the Mediterranean being richer than 

 the fauna of British seas, and the latter than those of the arctic regions. 



3 Quait. Journ. Geol. Soc. vol. xxvii (1871) p. 457. 



