PORTLAND EOCKS OF ENGLAND. 235 



Portland, and less common in corresponding beds at St. Alban's 

 Head. 



Note. — Of the fossils described from the Kimmeridge Clay (Quart. 

 Jouni. Geol. Soc. vol. xxi. p. 196) the name Inoceramus expansus 

 had been previously used, and must be changed for 1. rasenensis; and 

 Leda lineata had been previously described by Kigaux and Sauvage, 

 in the ' Journal de Conchyliologie,' under the title of L. venusta. 



EXPLANATION OF THE PLATES. 



Plate YIII. 



Comparative Sections of the Portland Eocks of England, with a generalized 

 theoretical section extending from St. Alban's Head to Buckinghamshire. 



Plate IX. 



Fig. 1. Natica incisa, Blake. Creamy limestones of Coney Hill. 



2. ceres, De Loriol. Creamy limestones of Coney Hill. 



3. Cerithium Hicdlestoni, Blake. Creamy limestones of Coney Hill. 



4. Eissoa acuticarina, Blake. Creamy limestones of Coney Hill. 



5. Cerithium hifurcatum, Blake. Swindon Sands, W, Swindon. 



6. Turbo Foucardi, De Loriol, Swindon Sands, W. Swindon. 



7. apertiis, Blake. Eoach, Portland. 



8. 8 a. Sowerbya longior, Blake. 8, Eubbly Umestones, Aylesbury ; 8 a, 



Swindon Sands, W. Swindon, 



9. Corbula saltans, Blake. Creamy limestones of Coney Hill. 



10, Myoconcha portlandica, Blake. Eubbly limestones at Coney Hill. 



11, Cypricardia costifera, Blake. Creamy limestones of Coney Hill. 



12, 12 a. Astarte polymorpha, Contejean. Swindon Sands, W. Swindon. 



13, 13 a. Cyprina impUcata, De Loriol. Eubbly limestones, Aylesbury, 



14, 14a, elongata, Blake, 2riyo7iia-heds, east of Swindon, 



1 6. Cardium ? calcareum, Blake, Portland chalk of Chicksgrove. 

 16. Ledal sp. Freestones, Swindon. 



Plate X. 



Fig. 1. Unicardium circulare, D'Orb. Eubbly limestones, Coney Hill, 



2, Cyprina swindoncnsis, Blake. Swindon Sands. 



3. Pecten Morini, De Loriol. Swindon Sands. 



4. Trigonia swindonensis, Blake. Swindon Sands. 



5. Astarte scemanni, De Loriol. Swindon Sands. 



6, Plicattda cchinoides, Blake. Eubbly limestone, Coney Hill, 



7, Ammonites triplicatus, Sow. Flinty series, Portland. 



8-8 d. Rhynchonella portlandica, Blake. Lower Portland Sand. 

 9. JDiscina Humphresiana, Davidson. Dwarf form. Lower Portland Sand, 

 Black Ven. ' 

 10. Fycnodus pagoda, Blake. Flinty series. Up way. 



Discussion. 



Mr. Htjdleston agreed generally with the author's conclusions ; 

 but he differed from him in one point — namely, in considering the 

 "roach" to constitute a good geological horizon, an uppermost 

 division of the Portlandian, characterized by the abundance of 

 CeritJiium and Cyrena. He quite agreed with Mr. Blake in his 

 reading of the Swindon section. He commented on the absence of 



b2 



