E. F. TOMES Otf THE GEEAT-OOLITE MADEEPOEAEIA. 169 



circumscribed. Illustrations of this may be seen in Chorisastrcea 

 and Phyllogyra. 



The operation of fissiparity has been very clearly explained by 

 Fromentel, and shown by him to be performed in two very distinct 

 ways. In the one the calice is divided into two or more parts by 

 the gradual approximation and union of two or more opposite septa. 

 This is fissiparity in the strictest sense of the word, and it cannot 

 be confounded with any other process. In the other process of fissi- 

 parity a gradual elongation of the calice first takes place, not merely 

 by the extension of the ends of the septa, but also by the lengthening 

 of the fossula — let me say, for the sake of perspicuity, in a direction 

 north and south. Constriction of the calice then takes place in the 

 opposite direction, that is to say, east and west. At this period the 

 calice makes some approach in form to the figure 8 ; and by degrees, 

 as the constriction continues, the calice is, so to speak, pinched in 

 two and the division is complete. It is this process of division 

 which has been confounded with gemmation ; and in massive serial 

 corals the two methods of increase are so very similar in appearance 

 that it is not at all easy to distinguish the one from the other. To 

 fully understand the distinction here mentioned, it is necessary that 

 fissiparity and gemmation should be studied at every period during* 

 their progress ; and when that cannot be done, the chances of an 

 erroneous conclusion will be very great. 



The species mentioned in this paper to which these observations 

 will apply most fully is the Chorisastrcea obtusa, which, until 

 removed by me from the genus Thecosmilia, was regarded as a 

 fissiparous species. 



Stratigraphical Position. 



The highly interesting and valuable collection of fossil corals 

 which has contributed so largely towards the material for the 

 following paper, consists of a beautiful and extensive series of 

 specimens in the possession of my friend Mr. T. J. Slatter, F. G. S., 

 of Evesham. They were collected near Fairford, Gloucestershire, 

 by his sister, Miss Slatter, whose attention was first directed to them 

 by the appearance of numerous corals scattered over the surface of a 

 ploughed field. Subsequently a great many unworn and beautiful 

 examples were obtained from excavations made for the purpose of 

 collecting specimens. 



I learn from her that some of these passed into the hands of Mr. 

 Brown, of Cirencester ; and that gentleman, in a communication 

 received some time since, informed me that many of the corals in 

 his collection spoken of as having been obtained at Cirencester, 

 really came from Fairford. It is more thau probable, therefore, that 

 some of those described and figured by Prof. Duncan, and stated to 

 be in Mr. Brown's collection, originally formed part of the Fairford 

 collection. 



Wishing for fuller information respecting the nature and strati- 



