182 MR. C. EEID AXD ME J. GEOTES OX THE [vol. Ixxvii, 



thinner being concave, the thicker flat or conyex on the exterior, 

 corresponding with the various stages in the development of the 

 lime-shell of living species. The calcareous accretion forming the 

 latter is built up by deposits on the concave inner wall of each 

 spiral cell ; hence in earlier stages, when it is thin, the whole lime- 

 shell presents a series of ridges ^^'ith rounded concave valleys 

 between, which latter gradually fill iip. until the whole space is 

 occupied, and the valleys have been transformed into rounded 

 ridges, while the former ridges have become fiirrows. 



In the case of the fossil fruits, when they break np, the spiral 

 portions separate most readily along their edges, long detached 

 pieces of individual spirals being frequently found, and when these 

 are fractured it is by a clean break transversely. AYhen a recent 

 lime-shell breaks, this is not usuallv the case, a fracture takins; 

 place more commonly quite irregularly across several spirals. This 

 difference may be due to the fact that the lateral walls of the spiral 

 cells, in the case of the Tertiary plants, do not break down so 

 completely before calcification, as in the recent species, and the 

 lime-shell, in consequence, is incompletely developed along the 

 sutures. 



We have found the oospore preserved in a few cases, mostly 

 in the gathering from the Basement-Bed Owing to the non- 

 preservation of the stalk-cell, there is an opening at the base of 

 the oogonium which is referred to in the descriptions as foramen 

 hasiJare. The walled-in space at the base of the oospore corre- 

 sponding to this is st3'led coJiors hasilaris. 



The fossil fruits are very diverse in shape, ranging from complete!}^ 

 globular (PI. 1\, figs. 1-8) to elongated ellipsoid, elongated 

 obovoid, and (PI. V, figs. 4 & 5) subcylindrical. In size the 

 diversity is also considerable, the length of those measured ranging 

 from about 325 to 1200 /x, and the breadth from 250 to 1C50^. 

 In colour, also, there is great diversit}^ ; but this doubtless is, to 

 some extent, due to the conditions under wdiich the fruits were 

 preserved. Some of the t^'pes of fruit resemble those of living 

 species. 



In the lime-shell of existing species we have seen no approach to 

 the remarkable papilliform processes found in some of the fossils, 

 to the cause and nature of which we have not at present discovered 

 any clue. The papilliform processes occur at more or less regular 

 intervals along the spiral cells. They Avere apparently first observed 

 by Sir Charles Lyell in fruits from the Bembridge Beds, described 

 and figured by him in Trans. Geol. Soc. ser. 2, vol. ii (1826) 

 p. 94, pi. xiii, figs. 7 & 8, under the name Cliara tuhercidaia. 

 Subsequent authors have described other species having similar 

 processes. Dr. Guido Stache, in his fine monograph on the fossils 

 of certain ancient Tertiar}' beds in the neighbourhood of Trieste 

 ('Die Liburnische Stuf e ' 1889), describes and figures six species 

 with this characteristic, and constitutes for them a section 

 Kosmogyra^, placing them under two genera, Kosmogyra and 

 KosmogyreJIa. 



A.mong living sj)ecies there are none with fruits quite like the 

 laro-e globose and sub-globose types figured in PI. IT, figs. 1-10. 



