324 Viscount (I'Archiac and M. de Verneuil 



distributed in the three epochs : the number of species increases from below upwards 

 in the following progression, viz. three are Silurian, nineteen are Devonian, and 

 forty-nine Carboniferous. The species in the first system are unimportant. Those 

 peculiar to the second are particularly developed in Devonshire and in the cor- 

 responding deposits of Paffrath and Villmar on the right bank of the Rhine, 

 although there are really very few species common to the two localities. The 

 P. expansa, Phil., P. monilifera, id., P. Defrancii, nob., and P. limbata, Phil., 

 lived through the two latter periods. The P. Delphinuloides, Goldf., and its 

 numerous varieties, seem also to belong to both systems. The Pleurotomaria, 

 which, with many other genera, are lost sight of from the coal-beds to the lias, 

 reappear in great number in the lower beds of the oolitic series and decrease 

 successively in the newer deposits, until they are represented in our present seas 

 only by the little genus Scissurella. 



The Trochi, much less abundant than the Pleurotomariee, are nevertheless dis- 

 tributed in the same manner in the three systems, whether in a horizontal or 

 vertical direction. The T. helicites, Sow. (in Murch. Sil. Syst.), is both Silurian 

 and Devonian. The T. Bouei, Stein.*, belongs to the second system in the south- 

 west of England, in the Eifel, and at Paffrath. The T. Yvaniif, Lev., appears to have 

 lived in the last two periods. The species of Turbo are more equally distributed 

 in the three systems. The TurritellcB of the ancient epochs are in general insuffi- 

 ciently characterized, in consequence of their having almost always lost the 

 mouth. Among the twenty-six species which now remain, of which it will un- 

 doubtedly be necessary to suppress some, three are Silurian, eight Devonian, and 

 fourteen Carboniferous. 



The Murchisonice \, on the contrary, are neatly characterized shells, and appear 

 to have been peculiar to the ancient beds : four species are Silurian, ten Devonian, 

 and four Carboniferous ; and three are both Devonian and Carboniferous ; namely, 

 the M. spinosa, Phil., M. angulata, id., and M. teeniata, nob. These shells are 

 particularly abundant in the Devonian beds of the banks of the Rhine. The 

 genus Loxonema^, which consists of shells formerly classed among the Terebra 

 and MelanicB, is also more exclusively Devonian. The L. rugifera and L. tumida, 

 Phil., are nevertheless found in the two upper systems. The Buccina, only one 

 species of which is noticed in the Silurian system, are less rare in the interme- 

 diate, and twelve are reckoned in the superior system. The B. acutum and B. im- 

 bricatum lived in large numbers during the Devonian and Carboniferous periods in 

 England, in Belgium, and on the banks of the Rhine. The B. arculatum, Schlot., 



* Mem. Geol. Soc. de France, tome i. f Ibid, tome ii. p. 39, 1835. 



-^ See posted, p. 356, and Bulletin Soc. G6ol. de France, tome xii. p. 154, 1841. 

 § Phillips, Pal, Foss. Cornwall, &c. p. 98, 1841. 



