OSTREA. 379 



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

 former being on the posterior side of the shell. 



The form with well-developed concentric ridges (Plate LVI, fig. 10), which 

 is abundant in the zone of Actinocamax quadratus, but ranges from' the zone of 

 Rhynchonella Cuvieri to that of Belemnitella mucronata, has been named 0. canalicu- 

 lata var. striata. 1 



Types. — Chama canaliculata, Sowerby, from the Upper Greensand of Shute, 

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

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

 Kopinge, Sweden. Exoyyra undata, Sowerby, from the Upper Greensand, 

 Blackdown, cannot be found. 



Distribution. — Hythe Beds (Bargate Stone) of Godalming. Lower Greensand 

 of Faringdon and Brickhill. 



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

 Schlcenbachia rostrata and Pecten asper) of the Isle of Wight (Ventnor, Niton, 

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

 Upper Greensand (Rye Hill Sands) of Warminster. 



Chalk Marl (zone of Schloenbachia varians) of Chiseldon. Cenomanian of 

 Wilmington, Devon. Zone of Holaster subglobosus of Fulbourn and Bur well. 



Zone of Rhynchonella Cuvieri of Harvet (Kent). Melbourn Rock of Hitchin. 



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



Zone of Holaster planus of Culver Cliff and Dover. 



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



Zone of Micraster cor-anguinum of Quidhamptom and Northfield. 



Zone of Marsupites testudinarius of Taplow. IJintacrinus band of Devizes 

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



Zone of Actinocamax quadratus of East and West Harnham, Whaddon, Marwell* 

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

 Brighton. 



Zone of Belemnitella mucronata of the Dorset Coast, Rogers Whiting Pit 

 (Fareham) and Alderbury well. 



Zone of Ostrea lunata of Trimingham. 



Ostrea semiplana, J.de C. Sowerby, 1625. Plate LVI, figs. 17 — 19. Plate LVII, 

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



1803. Ostracites sulcatus, /. F. Blumenbach. Specim. arehseol. tell., p. 18, pi. i, 



fig. 3. (Non. Ostrea sulcata, Born, 

 1778.) 



1 Eowe, ' Zones of the White Chalk. I, Kent and Sussex ' (1900), p. 345 ; Griffith and Brvdone, 

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



