76 Proceedings of the Royal Physical Society. 



The Carboniferous species of Co7iiilaria occurring in Britain 

 is C. quadrisulcata, and is very seldom found in a perfect 

 state. The proximal or larger end is usually crushed in- 

 wards, or broken short off at the margin. Mr James Bennie, 

 however, was successful enough to find an example with the 

 rhombic larger end partially closed by the bent down and 

 reflected margins, leaving a quadrangular opening in the 

 centre. The four corners of this opening form re-entering 

 angles, which join the four angles formed by the union of the 

 conical sides of the shell.* Whether this structure closed 

 the orifice of Comdaria or not, it is difficult to say. Did 

 it act the part of an operculum ? An allied form, Theca 

 02:)erculata (Salter),-!* from the L. Tremadoc beds, possesses 

 such an organ, and it is quite possible the inturned edges 

 may perhaps have at the least given support to some kind 

 of lid. To those possessing a large series of Conularice, 

 the study of the genus would well repay them, for it is 

 one of the forms of our old rocks of which we know 

 comparatively little. The shape of the shell somewhat 

 resembles that of some living Pteropods, although in the 

 matter of size it is simply a giant compared with tlie 

 latter. 



The CEniALOPODA, or highest class of the Mollusca, is re- 

 presented in the Carboniferous Limestone Series by the 

 smallest number of genera of any except tlie Pteroj)oda, 

 just referred to. The genera number six, and all apper- 

 tain to the Tetrabranchiate division of the class. The 

 greatest number of species occur in the genera Orthoceras 

 and Goniatites, but it is very probable, as too often happens 

 amongst Palaeozoic shells, that a number of these will dis- 

 appear from our records on a close and vigorous examination. 

 According to Messrs Armstrong and Young, the greatest 

 number of species are found in the upper group of lime- 

 stones, cliieily in the form of casts. Tlie best preserved 

 specimens come from the limestone shales, and frequently 



* See Ethcridge, Structure of Comdaria (Geol. Mag., 1873, x., p. 295). 

 t Mem. Geol. Survey, iii., p. 351, t. 10, f. 22-24. 



