110 JR. F. Tomes — Liassic Madrepor-aria. 



the calice is rubbed or worn down, these all disappear, and the 

 simple septa are seen to pass quite up to the columella. The sides of all 

 the septa have rather distant but well defined and prominent tubercles. 



Compared with Thecocyathus mactra, the present species differs 

 in its smaller size, its much more rugose epitheca, and in its pali, 

 the margins of which are much more tubercular. The tubercles 

 are undistinguishable from those of the columella, with which they 

 appear to blend. 



I may take this opportunity of observing that with access to a 

 considerable collection of specimens of Thecocyathus mactra, and 

 Thecocyathus tintinnabulum, as well as to a number of species of 

 Thecocyathus Moorei from the Upper Lias of Ilminster, I am not only 

 satisfied of the distinctness of the species from the Upper Lias of 

 Gloucestershire and Oxfordshire from the others, but am fully pre- 

 pared to follow M. de Fromentel in putting together as one species 

 Thecocyathus mactra and Thecocyathus tintinnabulum. 



I also avail myself of the present occasion to make a few remarks 

 on the genus Thecocyathus. Amongst the most ancient of the 

 Turbinolidce, this genus might not unnaturally be expected to possess 

 characters approximating it in a greater or less degree to the Lower 

 Mesozoic Astrceidce, with which in time it is so nearly associated. 

 None of the Turbinolidce have to my knowlege been met with in the 

 Lower or Middle Lias, but I may observe that although the Mont- 

 livaltia radiata, of Duncan, which occurs in the bottom of the Middle 

 Lias, or perhaps at the junction of the Middle with the Lower Lias, 

 has an abnormal and primitive number of primary septa, it never- 

 theless has a very thin epitheca scarcely obscuring the costas, 

 which is quite unlike that of any genus or species of older date. 



Again, the sides of the septa of Montlivaltia mucronata, which is 

 found associated with the last species, are ornamented with thickly 

 crowded flattened tubercles, instead of the vertical ridges which 

 characterize nearly all the Jurassic Montlivaltics. These peculiarities 

 seem to indicate some affinity in both these species with more recent 

 forms. 



In Thecocyathus tubercidatus we have a very modified development 

 of the inner ends of the principal septa, which is no doubt equivalent 

 to the growth of pali, and the same sort of development takes place 

 to a considerable though more limited extent in Thecocyathus Moorei, 

 for I observe that when the calice is ground or worn down, the pali 

 are with difficulty traceable. Some of the much worn specimens are 

 undistinguishable from Montlivaltice, having columellas formed by 

 the fusion of the septa in the centre of the visceral cavity. The genus 

 Thecocyathus must therefore, I think, he regarded as very sub-typical 

 of the Turbinolidce — the precursor, in fact, of the more typical genera. 



Nearly allied to Thecocyathus is Trochocyathus, but unlike the 

 former, which continued into the period of the Lower Oolite and 

 no longer, 1 the latter lived on through the Secondary and into 



1 I limit my remarks to such species of Thecocyathus as have been met with in 

 this country, one of which has been obtained from the Inferior Oolite of Dorsetshire. 

 M. de Fromentel describes four as occurring in the French Oolites. 



