OSTREA. :57'.> 



0. veskularls, the differences being accounted for by tlie attached surface in the 

 former being on the posterior side of the shell. 



The form with well-developed concentric ridges (Plate LVI, fig. ]0), which 

 is abundant in the zone of Actlnor.amnx quadratns, but ranges from the zone of 

 Rhi/nclionella Cavieri to that of Belnuiiitdht miicrdiuifd, has been named 0. canalini- 

 laia vai'. Kfrinta} 



Tijpc'i. — Cliama canal inilata, Sowerby, from the Upper Greensand of Shute, 

 near Warminster, is in tlie British Museum. 0. Ifitcralis, Nilsson, is from the 

 Upper Chalk of Sweden. Gliama conica, Nilsson, from the Upper Chalk of 

 Kopinge, Sweden. Exoyijra nndata, Sowerby, from the Upper Greensand, 

 Blackdown, cannot be found. 



Distribution. — Hj'the Beds (Bargate Stone) of Godalming. Lower Greensand 

 of Faringdon and Brickhill. 



Gault of Folkestone and Okeford Fitzpaine. Upper Greensand (zones of 

 SrhhruJjachia roffnita and Foctcn nxpnr) of the Isle of "Wight (Ventnor, Xiton, 

 Compton Bay). Upper Greensand (zone of SchlferiJmclna rostrata) of Blackdown. 

 Upper Greensand (Rye Hill Sands) of Warminster. 



Chalk ]Marl (zone of Sclila'iiIiarJiia varictnx) of Chiseldon. Cenomanian of 

 Wilmington, Devon. Zone of Holaster suliglnljosus of Fulbourn and Burwell. 



Zone of RJn/nchouella Cuvieri of Harvet (Kent). Melbourn Rock of Hitchin. 



Zone of Tcrehratiilina lata of Hampshire, the South Devon coast, and Dover. 



Zone of Holaster planus of Culver Cliff and Dover. 



Zone of Micraster cor-testudinarinm of Pinhay, Borstal, Seaford and Dover. 



Zone of Micraster cor-ancjuinum of Quidhamptom and Northfield. 



Zone of Marsupites testudinariu^ of Taplow. Uintacrinns band of Devizes, 

 Road (Salisbury), Holmwood Park (Keston), and the Thanet Coast. 



Zone of Actiiiocama.v qundrafus of East and West Harnham, Whaddon, Marwell 

 (Hants), Compton, Shawford, Fareham, West Meon, Mottisfont, Taplow and 

 Brighton. 



Zone of Belemuitrlla unicrouafa of the Dorset Coast, Rogers Whiting Pit 

 (Fareham) and Alderbury well. 



Zone of Ostrea hnmlii of Triniingliam. 



OsTREA SEMirr.AXA, J.de C. Sovy-rhi/, lc?2"). Plate T.VI, figs. 17— 11». Plate LVII. 

 Plate LVIII, figs. 1—5. Text-figures 183—193). 



1803. OsTRACiTEs srr.cATrs, /. F. Blinnenbarh. Specini. art-hseol. tell., p. 18, pi. i. 



fig. 3. (N<,iu. Oflrea nulrata. Born, 

 1778.) 



» Rowe, ' Zones of the White Chalk. I. Keut and Susse.v ' (1900), p. 34.5 ; Griffith and Biydone, 

 ' Zones of the Chalk in Hants ' (1911), p. 3. 



