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ritOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Nov. 21, 



prominent central ridge, produced behind into a thick blunt spine. 

 Posterior edge doubly emarginate, but with the angles scarcely at 

 all produced. Six longitudinal ribs on each side of the central one, 

 all closely tuberculate, so as to form transverse rows. 



The projecting mass is supposed to be the stem, and is nearly as 

 long as the frond, very thick, obtuse, attached to the posterior mar- 

 gin, and shaped like the siphon-sheath of a bivalve shell. 



Locality. Valley of Aceromarka. 



Bolivians, bipennis. PI. V. fig. 11. 



Mr. Forbes observed the other part of this specimen in the rock, 

 but could only detach one half. The outline is therefore added to 

 our figure. 



Frond semioval, emarginate behind, gibbous at the sides, and 

 with the posterior angles produced into strong divergent tapering 

 spines. Surface marked by ridges and furrows parallel to the 

 curve of the front and back margins. Spines also furrowed near 

 the base. Stem (apparently attached) long filiform. 



Locality. Valley of Unduavi, eastern slope of the Andes. 



The number of species that we recognize in this collection, made 

 with so much perseverance and at great personal hazard, are — 



5 Lower? Silurian (Bilobite-schists). 

 14 Upper Silurian (grey sandy schists and sandstones). 



3 Devonian. 

 13 Carboniferous. 



D'Orbigny's collection of Silurian fossils contained 10 species, of 

 which none have occurred to Mr. Forbes. They are — 



Cruziana rugosa. Phacops (Calymene) Verneuilii. 



furcifera. (C.) macrophthahna ? 



Orthis Humboldtii. Asaphus Boliviensis. 



Lingula marginata. ■ 



Adding these to our list, we obtain 27 or 29 Silurian species for the 

 Central Andes, belonging to a fauna specifically clifferent from that 

 of any other quarter of the world. I venture without hesitation to 

 assert that the identifications by D'Orbigny with European forms, 

 where I am acquainted with the species, are wrong. I am obliged 

 to say this much, since that distinguished author has fearlessly 

 united things which differ b}' the most obvious external characters, 

 and has lent the sanction of his great reputation, on such evidence 

 as this, to a former community of species, and an equable diffusion of 

 heat. In regard to the Carboniferous forms, where M. D'Orbigny 

 is unwilling to allow more than a close analogy between the two 

 continents, I am again compelled to differ from him, but it is in 

 an opposite direction. 



Summary. 



Muensterii. 



dubia. 



Graptolites dentatus. 



There is some doubt about both his 

 species of Phacops. They are probably 

 Devonian. 



