ON THE BRITISH FOSSIL COKALS. 151 



Division Tkochoctathace^. 

 Genus Tkochoctathtts. 



1. Trochocyathiis Ilarvei/anus, Ed. & H. 



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

 their ' Monograph of the British Fossil Corals,' part 1. p. 65. They associated 

 it with two species, which are, as they suggest, undistinguishable, viz. 

 Trocliocyatlms Konigi and Trochocyathiis Warhurtoni. The first of these 

 species is the TurhinoUa Konigi of Mantell. 



An examination of a series of specimens attributed to Trochocyathus 

 Harveyanus, Ed. & H., and the consideration of the value of the Trochocyathi 

 just mentioned, have led me to recognize five forms of Trochocyathi breves, 

 all closely allied and well represented by the original type of Trocliocyathus 

 Harveyanus, Ed. & 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 hemispherical ; all have four cycles of septa and the same propor- 

 tion of pali. These are the primary and most essential peculiarities of the 

 genus. 



The costse differ in their size, prominence, ornamentation, and relation to 

 the septa in some of the foims ; and the exsert nature of the septa, their 

 granulation, and the size of the corallum also differ. The structural differ- 

 ences are seen in many examples, and are therefore more or less persistent; 

 nevertheless it is found that whilst several specimens have the septa spring- 

 ing 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. The corallum is nearly double the size of the type ; its septa 

 are rather exsert, and are very granular. The costte are very prominent, 

 ridged, marked with numerous smaU. pits, and are continuous with the septa. 

 The epitheca is waved and well developed. The spaces between the larger 

 costse are more or less angular. The peduncle is large. 



Locality. Gault, Folkestone. In the British Museum. 



Variety 2. The corallum is as large as that of variety 1, but it is more 

 conical. The costse are less pronounced, and the septa, which are more 

 granular than those of variety 1, arise from the intercostal spaces. The 

 costal ends are very elegant in shape, and form a margin of rather sharp 

 curves. 



Locality. Gault, Folkestone. In the British Museum. 



Variety 3. The corallum is rather flat, but hemispherical. The septa are 

 not exsert, and they arise from the costal ends. The costse are equal : none 

 are more prominent than others. They are all rather broad, flat, and beau- 

 tifully ornamented with diverging curved hues. Their free ends are equal 

 and curved. 



Locality. Gault, Folkestone. In the collection of the Rev. T. Wiltshire, 

 F.G.S. 



