President's Address. 45 



The so-called division of the Monomyaria are coidiiied to 

 the inariiie limestones, the Avicidojpectinidce being the most 

 abundant and widely distributed group. The Dimyaria are 

 divisible into. two sections — one, comprising the truly marine 

 forms is confined to the Carboniferous Limestone strata, 

 the other or brackish water division, consisting of sucli 

 shells as Aiithracosia and AiithracojJtera, etc., is to b(i 

 found in the Coal Measures and other brackish or fresh 

 water strata.* 



The Carboniferous Bivalves do not enter into the composi- 

 tion of the limestones in anything at all approaching the 

 abundance of the Brachiopoda,i- but appear to have, in a 

 great degree, confined their habitat to the more argillaceous 

 deposits of the period. The marine species " are met with in 

 greatest numbers in the shales and clay ironstones that alter- 

 nate with the limestone." I 



Casts of the interior of the valves, or specimens from which 

 the external shell has been dissolved away by chemical 

 action, should be eagerly sought ; for, on the study of these, 

 and facts revealed by their study, will depend the entire 

 future classification of the group. 



The family Ostreidcc is not satisfactorily established in 

 Scotch Carboniferous rocks, § although it is represented in 

 Ireland by an Anomia,\\ in Belgian beds by a true oyster, If 

 and in the American Sub-Carboniferous by a shell which 

 has been so referred.** 



Formerly the Pcctinidcc were united with the Ostreidcc, 

 but by many good authorities they are separated as a dis- 

 tinct family.f-I- Further, Messrs Meek and Hay den have 



* Armstrong and Young, Catalogue, p. 44. 



+ Craig, Trans. Geol. Soc, Glasgow, vi., pt. 1, p. 6. 



X Armstrong and Young, Cat. W. Scot. Foss., p. 50. 



§ I am not prepared to maintain the identity of the shell I some years ago 

 called Anomia antiqua, M'Coy (]\[em. Geol. Survey, Scotl., Expl. 22, p. 38). 



II A. antiqua, M'Coy (Synopsis, 1844, t. 19, f. 7). 



II Ostrea nohilissima, De Koninck (Foss. Terr. Carb. Belgique, Suppl., 1851, 

 p. 680, t. 57, f. 1). 



** 0. liatcrcula, Winchell (Proc. Acad. Nat. Science, Philadelphia, 1865, 

 p. 124). 



+t Stoliczka, Mem. Geol. Survey, India, 1871, iii,, p. 423. 



