226 Geological Society, 



The author describes and gives engravings of two species of these 

 fossils, with comparative sections of the recent Zamia and Cycas. 



1. In the larger species, which he calls Cycadeoidea megahphylla, 

 the bases of the leaves are two inches long, and have nearly the form 

 and size of those of the Zamia horrida. The trunk is short, and has 

 a deep central cavity, like the interior of a bird's nest,— in which a 

 number of siliceous plates intersect one another, and form an irre- 

 gular plexus, unlike any vegetable structure, but resembling the 

 coarse cellular appearance that is common in fossil wood. Nearer 

 the circumference there appear distinct organic radiations, disposed 

 in an insulated circle, — like that in the trunk of a recent Zamia, but 

 differing, in that it is much broader, and placed nearer the circumfer- 

 ence of the stem. The larger plates of this circle are made up of 

 smaller plates, almost invisible to the naked eye. Between this radi- 

 ating circle and the outer case or leaf stalks, is a narrow band, com- 

 posed of a minutely cellular, and nearly amorphous substance, but 

 analogous in structure and position to a much broader band that is 

 exterior to the radiating circle of the recent Zamia. 



2. In the second and smaller species {Cycadeoidea microphylla) , 

 the bases of the leaves are about an inch in length, but small and 

 numerous, much like those of the Xanthorrhceat or Gum Plant, of New 

 South Wales. The trunk is more elongated, and the cavity at the 

 summit less deep, whilst the transverse section exhibits the same irre- 

 gular net-work at the centre, but near the circumference has two 

 concentric circles composed of radiating plates ; and exterior to each 

 of these a narrow ring devoid of plates, — analogous to the two lami- 

 nated circles within two cellular circles in a recent Cycas. 



In external and internal structure, these plants approach more 

 closely to the existing family of Cycadece than to any other ; and 

 they supply, from the fossil world, a link to fill the distant void which 

 separates the Cycadece from the nearest existing family, the Coniferce. 

 Their occurrence in the Portland oolite adds another to the many 

 facts which indicate the climate of these regions, during the period of 

 the oolitic formations, to have been similar to that of our tropics. 



A letter to the President was read, from Gideon Mantell, Esq. 

 F.G.S. &c. inclosing a list of the fossils of the county of Sussex. 



This list, which is taken principally from specimens in the author's 

 own collection, enumerates the fossils, first, of the alluvial and dilu- 

 vial deposits j and, successively, those of the London clay, the plas- 

 tic clay, chalk, chalk-marle, firestone, gault, Shanklin sand, and Hast- 

 ings deposits, including the Ashburnham beds. 



Subjoined is a comparative table j one of the most remarkable fea- 

 tures of which, is the preponderance of the number of species in the 

 marine formations over those of the beds assumed to be of fresh-water 

 origin, in a ratio of not less than six to one ; the testaceous mollusca 

 forming two-thirds of the whole, while in the fresh-water strata, the 

 proportion is reversed. Thus the marine deposits contain upwards 

 of two hundred and forty species of shells, and the two fresh-water 

 formations but twenty-two species. In the other classes and orders, 

 equally striking differences are observable. 



On 



