116 M. Barrande on the Silurian System of Bohemia. 



ras, 8 to 9 species ; Gomphoceras, 14 to 16 species ; Trocho- 

 ceras, 14 to 16 species ; Cyrtoceras^ 65 to 70 species ; and 

 Orthoceras, 95 to 100 species. Some forms of the last two 

 genera fill whole beds with their remains, but most of the 

 other species, especially of the genera first mentioned, are 

 rare. The occurrence of Nautilus in this early stage is, 

 however, well established. The Pteropods of the genera 

 Conularia and Pugiunculus have now undergone a marked 

 decrease, and the Heteropods only furnish a few species of 

 Bellerophon. The Gasteropods have their maximum in this 

 stage, in 70 to 80 forms, of which 20 are referred to the 

 genus Capulus; among the other types occur Euomphalus, 

 Natica^Murchisonia,Pleurotomaria, Turbo, Turritella, he. As 

 a remarkable peculiarity may be noted one species of Turbo ? 

 and two of Euomphalus, furnished with their operculum. 

 The Acephalse also shew a richness of forms hitherto unex- 

 ampled in Silurian countries ; numbering about 80 species in 

 the genera Cardiola, Avicula, Mytilus, Cardium, Tleurorhyyi- 

 cus, &c. &c. The Brachiopods also increase rapidly, 64 

 species being distributed in the following genera, thus : Te- 

 rebratula 26, Pentamerus 2, Spirifer 12, Orthis 7, Leptcena 

 11, Chonetes 1, Orbicula 4, Lingula 1. A few species of En- 

 crinites, but in incalculable numbers, represented the Echi- 

 noderms. The Zoophytes were from 25 to 30, including 10 

 or 12 Graptolites, — these problematical bodies disappearing 

 in the lower part of this, as they only appeared in the upper 

 part of the former stage. The genera of Polyparia observed 

 in Bohemia, and even the species, are chiefly those known 

 in England, as especially the Calamopora, Porites, Cyathophyl- 

 lum, Catenipora, &c. 



We already noticed the occurrence of Graptolites asso- 

 ciated with several upper Silurian forms in some calcareous 

 nodules, imbedded in the black slates of the last stage D. 

 These beds are covered by strata more than 1200 metres thick, 

 before the same species again appear in this upper stage. 

 Either, therefore, the same specific forms have been twice 

 created in this locality, or they have twice immigrated into 

 this basin, at distant periods, from some other locality. The 

 author adopts the latter view, and regards the earliest of 

 these beings as a kind of colony sent out to explore an un- 



