32 



BRITISH FOSSIL CORALS 



A very interesting variety of this species is in the Rev. T. Wiltshire's Collection, and 

 has its costse running obHquely to the long axis of the corallum. They are profusely 

 granulated (PI. XII, figs. 8, 9). 



Division — Trochocyathace.e. 

 Genus — Thochqctathus. 

 1. Trochocyathus }lxK\mk^\Js, Ed. cmd H. 



This species was described by MM. Milne-Edwards and Jules Haime in their' Mono- 

 graph of the British Fossil Corals,' Part I, p. 65. They associated it with two species, 

 which are, as they suggest, indistinguishable, viz. Trocliocyalhns Koenigi and Trocliocya- 

 tlms Warburtoni. The first of these species is the Tarhinolia Koenigi of Mantell. 



An examination of a series of specimens attributed to TrochocyatTius Harveyanus, Ed. 

 and H., and the consideration of the value of the TrochocyafM just mentioned, have led me 

 to recognise five forms of Trochocyathi breves, all closely allied and well represented by 

 the original tj^pe of Trochocyathus Harveyanus, Ed. and H. When placed in a series with 

 this Trochocyathus at the head, there is a gradation of structure which prevents a 

 strictly specific distinction being made between the consecutive forms ; but when the 

 first and the last forms are compared alone, no one would hesitate to assert that there is 

 a specific distinction between them. All the forms are simple, short, and almost hemi- 

 spherical ; all have four cycles of septa, and the same proportion of pali. These are the 

 primary and most essential peculiarities of the genus. 



The costge diff'er in their size, prominence, ornamentation, and relation to the septa in 

 some of the forms ; and the exsert nature of the septa, their granulation, and the size of the 

 corallum, also differ. The structural differences are seen in many examples, and are 

 therefore more or less persistent ; nevertheless it is found that, whilst several specimens 

 have the septa springing from intercostal spaces instead of from the ends of the costae, one 

 or more, having all the other common structural peculiarities, present septa arising from 

 the costal ends. This method of origin can hardly constitute a specific distinction. I 

 propose to retain Trochocyathus Harveyanus as the type of a series of forms the sum of 

 whose variations in structure constitutes the species. 



Variety 1 (PI. XIII, figs. 1, 2). — The corallum is nearly double the size of the type ; its 

 septa are rather exsert, and are very granular. 



The costse are very prominent, ridged, marked with numerous small pits, and are 

 continuous with the septa. 



