iSgg.] Eoord. — Carboniferous Brachiopoda and Mollusca. 8i 



them. In Spirifcr the most striking feature is undoubtedly 

 the spiral cones, already referred to, attached to the smaller 

 valve. These are but rarely seen, though they may sometimes 

 be developed by the rough and ready method of filing away 

 the shell of the larger valve. Only shells filled with crystalline 

 calcite will yield good results, to attain which both patience 

 and skill are required. 1 Externally Spirifers are generally 

 radiatingly ribbed, but there are also smooth species. The 

 large valve has a median depression, and there is a corres- 

 ding elevation in the small one. This is a feature common 

 to many Brachiopod shells. Athyris, like Spirifer, is a "spire- 

 bearer," and its spiral cones are similarly constructed, except 

 as to certain details of their loop-like supports. None of 

 the three genera — Productics, Spirifer, Athyris — now exist. 

 1 ' ercbratula and Rhynchonella, however, are represented, 

 though perhaps sparingly, in modern seas ; the ancient shells 

 differ but little from their modern descendants. In both 

 these genera the brachial supports are of more simple con- 

 struction than in Spirifer and Athyris, consisting only of the 

 loop-like structures. 



To geologists the Brachiopods are of great importance, as 

 they not only indicate the marine origin of the beds in which 

 they are found, but also by the persistence of certain species 

 in similar beds enable widely separated deposits to be 

 correlated. The Stringocephalus Limestone (Devonian) of the 

 Eifel, for example, derives its name from a Brachiopod which 

 is found in great abundance in it, and by means of which this 

 deposit may be recognized wherever it occurs. 



Passing now to the Mollusca, some of the most prevalent 

 genera of L,amellibranchs in the Carboniferous Limestone 

 are Pecten, Aviculopecten, Cardiomorpha, Conocardium, and 

 Edmojidia. The first of these has retained its distinguishing 

 features from its early appearance in the Devonian seas to the 

 present day, and is familiarly known as the " comb-shell" or 



1 An elaborate method of developing the brachial apparatus of Brachi- 

 opods was invented and practised with much success by the late Rev. 

 Norman Glass, in which a file, a knife, and some dilute acid were the 

 agents employed. The process is described in the Memoirs of the 

 Paheontographical vSociety, vol. xxxvi., 1882, Foss. Brach., Suppl. 

 vol. v., part I. ; copiously illustrated. 



