TJPrER GREENSAND AND CHLORITIC MARL. 



371 



allow a large relative proportion of the plastron to the under- 

 surface of the portable dwelling. 



The constituents of the plastron are in normal number, as in the 

 typical Emydians ; there are no accessory pieces interspersed 

 between the hyo- and hypo-sternals, as in the Wealden genus 

 Pleurosternon. 



The precise measurements, together with figures and minute 

 description, will be published shortly. In the meantime the fact of 

 the discovery of a freshwater Tortoise in the Upper Greensand is of 

 interest, throwing additional light on the conditions of life in that 

 epoch, and involving either the proximity of a continent or the 

 remains of island faunas distributed in the marine deposits. 



The Crayfish obtained by Saxby, figured in Prof. Bell's Pono- 

 graph of the Crustacea, and the Chelonian found more recently by 

 Mr. Norman, evidently prove that more thorough investigations 

 among these chert rocks might result in further important additions 

 to the Greensand fauna. 



The next 20 feet of compact red sand are for the most part 

 unfossiliferous ; or rather the organic remains have been nearly 

 obliterated. It is harder in texture than the succeeding 4 feet. 

 Without any other lithological change than hardness, we suddenly 

 come to a zone in which well-preserved casts of Mollusca abound, 

 differing, as will be noted, from the Upper Cherts and Rags in a 

 remarkable manner. At the base of this (that is, 20 feet from the 

 lowest chert nodules) an Ammonite occurs, which, so far as I can 

 discover, has not been described. Two specimens found by Capt. 

 Ibbetson are now in the Jermyn-Street Museum, unnamed ; a third 

 is now in the Natural-History Museum, South Kensington, in 

 my Isle-of- Wight collection, recently purchased by the Museum 

 authorities. It has been placed provisionally by Mr. Etheridge as 

 a species between A. auritus, and A. rostratus ; though I think it 

 will be found to differ from both sufficiently to rank as a new 

 species. It is invariably of the same size, from 2| to 3 inches in 

 diameter, and remarkably thin for its size, not having the pro- 

 minent tubercles of A. auritus or the sharply defined chambers of 

 A. rostratus. At the back the markings are alternate, more resem- 

 bling the Gault species A. interruptus. Dr. Wright, of Cheltenham, 

 was unable to identify my specimen with any species known to him. 



Immediately above, though never intermixed, the following 

 fossils are found : — 



Ammnnites auritus, Sow. 



rostratus, Sow. 



Trigonia aliformis, Park. 

 T. ornata, D'Orb. 



vicaryana, Lyc. 



Panopsea plicata, Sow. 



mandibula, D'Orb. 



Plieatula pectinoides, Sow. 

 Ostrea canaliculata, D'Orb. 

 Pecten orbicularis, Sow. 

 Gardium Grentianum, Sow. 



Area carinata, Sow. 

 Cucullaea glabra, Park. 



fibrosa, Sow. 



Natica sp. 

 Ciuulia sp. 



Vermicularia eoncava, Sow. 

 Ehynchouella latissiraa, Dav. 

 Terebratula biplicata, Brock. 

 Modiola sp. 

 Serpula antiquata, Sow. 



