PALEOZOIC FOSSILS OF THE ASTURIAS. 67 



pression, between pentagons more or less rounded and ellipses more 

 or less elongated ; but at length departing from this character, we 

 find the transverse direction predominate in T. Ezquerra^ by the 

 extreme elongation of the two lateral folds which we have traced 

 from their first origin in T. Campomanesii through their further 

 development in T. Fetronesensis. At the same time, the angle at 

 the apex becomes more open, the ventral furrow is as deep as the 

 dorsal one, the general contour of the shell becomes heptagonal, and 

 its surface becomes divided into five parts, which are hollow and 

 unequal, but disposed symmetrically on each side of the axis, and 

 corresponding on the two valves. The T, Hispanica is simply the 

 result of a still greater extension, and of an elevation of the lateral 

 folds, which in it become confounded with the hinge, which is 

 straight and very long, as in the winged Spirifers. The angle at the 

 apex is nearly equal to two right angles, and the medial furrow is 

 always as deep as the sinus. Lastly, the variety (a) of T. Hispa- 

 nica presents the concluding term of this series of transformations, 

 which, commencing with a suborbicular shell, has conducted us gra- 

 dually to a form very nearly resembling that of a Solen. 



We have paid every attention in determining these species ; and 

 the examination of a considerable number of individuals of each of 

 them, in various stages of growth, induces us to think that the di- 

 stinctions we have established are well founded, and that they will 

 be confirmed by future investigations. Among the species, T. Pe- 

 lapayenfiis occurs both in the Ural and Eifel Devonian beds, and 

 T. Ezquerra in the limestones of Nehou (Manche). 



If we inquire concerning the localities already known of the other 

 fossils in the preceding list, we find that T. Adrieni occurs in the 

 Eifel limestone, T. reticularis is common to the Silurian and Devo- 

 nian rocks of the north and east of Europe, and T, Daleidensis ap- 

 pears in the grauwacke of the banks of the Rhine. Among the 

 Spirifers, one variety of S. heteroclitus and a variety also of aS'. Ver- 

 neuili are confined to Devonian beds ; and the three other species, 

 which are as yet peculiar to the Asturias, recall to mind by their 

 transverse form and simple plications the characteristics of the genus, 

 especially as developed during the Devonian period. All the three 

 species of Orthis are known : O. crenistria is a Devonian form, O. 

 resiipinata both Devonian and Carboniferous, and O. orbicularis 

 Silurian ; but with regard to the latter, there is some doubt still as 

 to its identity. Of two species of LeptcBna^ one, L. Dutertrii, is 

 common in the Devonian beds of the Bas Boulonnais ; and the other, 

 a variety of L, Murchisoni, the type of which occurs in the grau- 

 wacke of Siegen, is somewhat widely spread in the ancient lime- 

 stones of Brittany and Normandy. 



Among the Polyparia of Ferrones, three are species common to 

 Silurian and Devonian rocks, and two are exclusively Devonian. 

 Serpula omphalotes is one of the most characteristic of the Devo- 

 nian fossils both in Western Europe and in various parts of Russia; 

 and, lastly, the presence of two species of Pentremitcs, a genus 

 hitherto unknown in the Silurian system, furnishes a still further 



VOL. II. PART II, G 



