TRANSLATIONS AND NOTICES 



OP 



GEOLOGICAL MEMOIRS. 



The Silurian Cephalopods of Bohemia ; and the Grouping of 

 Orthoceratites. By Joachim Barrande. 



[System e Silurien du Centre de la Boheme, par Joachim Barrande. l^re 

 Partie. Kecherches Paleontologiques. Vol. ii. C^phalopodes, 3nie s^rie, pi. 

 245-350. Formes droites. Grroupement des Orthoceres.] 



In this series, M. Barrande describes the straight forms of the 

 Silurian Cephalopods of Bohemia, which include the genera BactnteSy 

 Bathmoceras, Treioceras, and Orthoceras, this last division comprising 

 the subgenera Huronia, Endoceras and Oonioceras. 



The three types Bacirites, Bathmoceras, and Tretoceras are repre- 

 sented in the Bohemian basin bj only 4 species; the subgenus 

 Endoceras furnishes only 2 representatives (0. pererjrinum and 0. 

 novator) ; while the subgenera Ilwonia and Gonioceras do not exist 

 in Bohemia. 



Of 430 species or varieties of the genus Orthoceras, about one-half 

 are figured in the present series. It was the intention of the author 

 to propose a classification of this genus corresponding as nearly as 

 possible to the natural order of its species ; but the hope of being able 

 to complete his researches among some of the most important forms 

 at present but imperfectly known, and the difiiculty of arriving at a 

 satisfactory arrangement, have decided him to propose a provisional 

 classification. 



This classification consists in grouping the Orthoceratites accord- 

 ing to the most salient characters, either of general form or external 

 surface. These superficial or external characters are not founded 

 upon the variations of the principal organs of the moUusks, which 

 it would have been desirable to takeas the basis of subdivision. 

 The almost invariable conformation of the aperture in Orthoceras 

 does not furnish any means of distinction derived from the form 

 of the head and of the arms or appendices ; and the inaccessibility 

 to observation of the elements of the internal structure of the 

 shell seems to reduce the grouping of this type to the employment 

 of the difi'erences which are observable in their external appear- 

 ance. By this arrangement the species of this genus are first of 

 all separated into two principal sections, founded upon their general 

 conformation — the one having a short cone, with an apical angle 

 relatively large, the other having a prolonged cone with the apical 

 angle relatively small. 



These two sections are distinguished by tlje names of short-coned 

 Orthoceratites {Orthoceres hrevicones) and long-coned Orthoceratites 

 {Orthoceres longicones). To facilitate the study of the forms of the 



VOL» XXIV. PART II. D 



