18 GEOLOGICAL MEMOIRS. 



The Silurian Pteropods of Bohemia. By M. J. Barrande. 



[SystSme Silurien du Centre de la Boheme. Par Joachim Barrande. l^re Partie : 

 Eecherches Paleontologiques. Vol. iii. Classe des Mollusques. Ordre des 

 Pt6ropodes. 4to. pp. 179, and 16 Plates. 1867.] 



Before describing the genera and species of Pteropods which cha- 

 racterize the Silurian deposits of Bohemia, M. Barrande gives an 

 historical resume of the successive discoveries of the genera of this 

 order from the year 1818, when Sowerby published the figures and 

 descriptions of two species of the genus Conularia, up to the present 

 time, when nine genera of Palaeozoic Pteropods are admitted by the 

 author, namely : — 



Species. 



Conularia, Miller, Sowerby 83 



Tentaculites, Schlotheim 52 



Hyolithes, Eichwald 84 



Hemiceratites, Eichwald 3 



Coleoprion, Sandberger 4 



Pterotheca, Salter 7 



Salterella, Billings 3 



Styliola, Lesueur, Ludwig 9 



Fhragmotheca, Barrande 1 



246 



These nine genera may be arranged in two divisions, according to 

 their relative importance. The principal or cosmopolitan genera, 

 those which are distinguished by the great number of their species, 

 by their great vertical extension in the Palaeozoic series, and by 

 their great horizontal diffusion over the surface of the globe, are 

 Conularia, Hyolithes, and Tentaculites. To these the author joins 

 Pteroiheca, because of its appearance on the two continents, namely, 

 in the United States, Canada, England, Ireland, and Bohemia. The 

 five other genera enumerated in the table are considered secondary 

 or local, because of the relatively small number of their species, and 

 especially because of their limited diffusion, both vertically and 

 horizontally. 



All these types are not met with in any one of the Palaeozoic 

 regions. Bohemia occupies the first place, possessing seven of the 

 nine genera enumerated ; while the Ehenish Provinces, with five 

 genera in the Devonian deposits, occupy the second place. The 

 United States, the British Isles, and Russia, although containing 

 the greatest Palaeozoic deposits, have not yet furnished more than 

 four types each. 



The two genera (Hemiceras and Salterella) which are wanting in 

 Bohemia are characterized by a peculiarity which caused the author 

 to hesitate before admitting them among the Pteropods, and which 

 consists in the extraordinary thickness of the partitions of the shell, 

 whilst the internal cavity is extremely reduced. This was the more 

 to be observed, since the remarkable tenuity of the testaceous 

 envelope in Conularia, Tentaculites, Coleo^rion, Hyolithes, &c. was 

 one of the principal reasons which induced scientific men to class 

 these types among the Pterojjods. The thickening of the shell of 



