58 GEOLOGICAL MEMOIRS. 



ribs divide. In the carboniferous limestone of Russia near 

 Moscow, and on the Dwina. 



7. Spirifer crassus, De Verneuil, Russia, pi. 6. fig. 2. Seven or eight 



ribs in the sinus, which towards the beak unite in two. The 

 dichotomy of the lateral ribs appears only on very few. De 

 Koninck's Sp. crassus, on the contrary, has no dichotomy of 

 the ribs. In the carboniferous limestone of Cosatschi-Datschi 

 in the Ural. 



8. Sp. JBlasii, De Verneuil, pi. 6. fig. 9. The hinge-border is 



shorter than the breadth of the valves ; in this respect the 

 only instance of the kind. The dichotomy of the ribs is very 

 distinct. From Kirilow in the Zechstein. 



9. Sp. fasciffer, Keyserling, Petschora, pi. 8. fig. 3. The ribs 



are divided into diverging bundles (biischelformig), the hinge 

 broader than the valve. Upper carboniferous limestone on 

 the Soiwa. 



10. Sp. striatus, with very distinct dichotomy of the numerous 



ribs. It has never yet been wanting where the carboniferous 

 limestone occurs in considerable extent, and Sp. mosquensis, 

 probably a mere variety of Sp. striatus, even distinguishes 

 the upper beds of the carboniferous limestone in Russia, in 

 opposition to the Productus giganteus characteristic of the 

 lower strata. 



11. Sp. duplicostatus, Phil., Yorkshire, vol. ii. pi. 10. fig. 1. 



12. Sp. semicircular is, Phil., Yorkshire, vol. ii. pi. 9. figs. 15, 16. 



Both from the carboniferous limestone of Yorkshire. 



13. Sp. Stockesi, Strzelecki, Phys. Descr. of New South Wales, 



pi. 15. fig. 1. 



14. Sp. Tasmanni, Strzelecki, pi. 15. fig. 2. Both from the carbo- 



niferous limestone of Van Diemen's Land. 



15. Sp. undulatus, a characteristic shell of the Zechstein in Northern 



Germany and England. 

 Besides the division of the ribs, all these Spirifers have this in 

 common, that their area never stands upright in an even surface, as 

 is so remarkably the case with Sp. cuspidatus and similar species, but 

 that this area is always curved, and in great part even concealed by 

 the beak, which is sometimes far curved over. But in this position 

 the remarkable triangular opening from the beak to the hinge-border 

 is never grown up, but always open. Only openings on even vertical 

 areas permit this angular growing up to be observed. In them alone 

 do lamellae proceed from the point towards the hinge, which being 

 concave towards the hinge, leave only a small opening towards the 

 hinge-border, for the passage out of the filaments of the tendon by 

 which the animal fastened itself to foreign bodies. M. de Verneuil 

 (in his description of the Russian species of Orthis and Spirifer in 

 Murchison's Russia, vol. ii.) has not sufficiently attended to this ; he 

 has forgotten the beautiful law of the correlation of organs, which led 

 Cuvier to such surprising and splendid discoveries, and which has 

 been developed in such an intelligent, lively and clear manner by 

 riourens in his work on Cuvier (Cuvier de Flourens, p. 151). He 

 maintains that the deltidium of the Terebratulae which pushes the 



