180 



THE GEOLOGIST. 



it, but I believe be thinks so, and it is a very excellent suggestion— 

 for tbe sbape is very like/* m . 



But in tbe lower part of tbe coal-formation, and m one or two 

 beds also in the upper portions, there are none but truly sea-shells. 

 It would take long to enumerate them; but I need only mention 

 one or two familiar names. Avicula, or rather a shell between Avicida 



Fig. 6. — Aviculopecten papyraeeus, Sow. 



Fig. 7 '.— Goniatites Listeri, Sow. Fig. 8. — Productus semireticidatus, Martin. 



(the pearl oyster), and Pecten (the scallop), and therefore called 

 Aviculopecten, fig. 1. Goniatites, fig. 2, a shell which is a near relation 

 to the nautilus. The nautilns itself is common enough. Nucula, 

 a true sea-shell, is with them; and, to name no more, the Productus 

 (fig. 3), which is found everywhere in the mountain limestone, must 

 have been deposited in sea-water — and deep sea, too — for it is found 

 with corals and fish, sea-faus and sea-lilies ; and belongs to a group 

 of shells which never quits the open sea. 



Perhaps we need not dwell upon the shells any more ; suffice it 

 that those of the bottom of the coal-measures are all marine, and 

 those of the top parts are not much like freshwater ones, and from 

 the company they keep, were probably marine too. 



* This author, Rudolph Ludwig (Dunker and Meyer's PalEeontograpkica, vol. 

 8, pi. iv., v. ; and vol. 10, pi. bod., lxxii.), in his papers on the "Naiades of the 

 Ooa] Measures of Westphalia," thinks he has detected the freshwater shells 

 Cyrena, Anodon, Unio; all of which are, I believe, Anthracosia ; and also Dreis- 

 Si one of which at least is an Anthracomya. He also quotes PlanorUs ! but 

 the little shell which goes under this name is the Sjpirorbis, mentioned further on. 



