300 li. F. Tomes — British Cretaceous Madreporaria. 



The comparative frequency of some of the species is as follows : — 

 Farasmilia centralis ... ... ... ... 200 



■ — ■ Grare/isis ... ... ... ... 4 



JIc/Htelli 38 



Coelosmil i a (both, iovms) ... ... ... ... 64 



Caryo2}hiiUia cylindracea ... ... ... 12 



The small Madreporaria of the Gault are so beautifully preserved 

 externally, and, from the cavity of the calice being almost always 

 obscured, are so difficult to examine internally, that a few words on 

 the best method of investigating their inner parts will not be out of 

 place. To begin with, all idea of washing out the calice may be 

 at once dismissed as altogether impracticable. Then there is the 

 breaking up of the corallum in the hope that a fortunate fracture 

 may reveal what lies in the bottom of the calice, which sometimes 

 pi'oves successful. But it is very uncertain work, and the following 

 method of examination may with advantage be adopted in its stead. 



Take a spoonful of fine plaster of Paris and well mix with it 

 a sufficient quantity of lamp-black to make it of a pale slate colour; 

 add water until it is of the consistency of thick cream. With this 

 fill a small box — an ordinary pill-box will do very well — and place 

 the coral, which must have been carefully removed from its matrix 

 of Gault, vertically in it, with the calice only exposed. It should 

 then be allowed not only to set, but to become thoroughly dry, when 

 some thin gum-water must be dropped into the calice, and again -be 

 allowed time to dry. The whole can then be rubbed down until the 

 bottom of the calice is exposed. I have found fine sand-paper, kept 

 flat b}'^ attachment to a strip of wood, a good thing to rub down with, 

 but great care must be taken to keep all the dust raised by the 

 operation blown away as fast as made. A common blowpipe will 

 do that quite successfully. If there is no destructive pyrites or hard 

 phosphate present in the calice, the coral will then be seen in section, 

 and present the appearance of a well-defined white figure on a dark 

 ground, and the presence or absence of a columella or pali can be 

 at once determined. It is the nearlj'^ white colour of the substance 

 of the coral itself which renders desirable the mixture of lamp-black 

 with the plaster, which, with a little care, will when dry have very 

 nearly the same colour as the Gault matrix. 

 Bathycyathus Sowerbyi, Edw. & Haime : Brit. Fos. Cor., 1850, 



p. 67, pi. ii, fig. 2. 

 Smilotrochus elongatns, Dune, (in part) : Supp. Brit. Fos. Cor., 1869, 



pt. ii. No. 1, p. 19, pi. vi, figs. 1-6. 

 Trochocjjathus conulus, Jukes-Browue (not Phillips) : Quart. Journ. 



Geol. Soc, 1875, vol. xxxi, p. 303, pi. xiv, figs. 14-16. 

 After a most painstaking examination I am fully satisfied that all 

 the specimens of the so-called Smilotrochus elongatus from the 

 Coprolite Bed of the Cambridge Greensand must be referred to 

 Bathycijathus Sowerbyi, and not, as was supposed by Mr. Jukes- 

 Browne, to Trochocijatlnis conulus, and my reasons for arriving at 

 that conclusion are as follows: — The broad and spreading foot 

 which is so well shown in Mr. Jukes-Browne's figure (tig. 14) 



