TRANSLATIONS AND NOTICES 



GEOLOGICAL MEMOIRS. 



On the Silurian Cephalopoda of Bohemia. 

 By M. J. Barrande. 



[Leonhard u. Bronn's N. Jahrb. fiir Min. u. s. w. 1854, pp. 5-12.] 



The following notices of the Silurian Cephalopoda of Bohemia form 

 part of a memoir by M. Barrande, a translation of the chief portion 

 of which appeared in No. 38 of the Journal, Miscell. pp. 5-10. 



M. Barrande enumerates ten genera of Cephalopods as occurring 

 in the Silurian rocks of Bohemia, viz. 



Nautilus. Gyroceras. Orthoceras. Gomphoceras. Ascoceras. 



Lituites. Trochoceras. Cyrtoceras. Phragmoceras. Goaiatites. 



The author's tabular view of the distribution of these genera in 

 the Stages D, E, F, G, and H of this formation is given at p. 8, 

 Journ. No. 38, Miscell. 



1 . Nautilus. — Although this genus has long been known to occur 

 in the Silurian formation, I do not know of any of its species occur- 

 ring at a lower level than the base of my upper division (Stage E) . 

 Here it makes its first appearance ; but it then disappears, and is 

 not found throughout the higher limestone groups. 



This Silurian genus has afforded me the opportunity of observing 

 the development, so to say, of three species from the embryonic con- 

 dition up to maturity. The embryo (fig. 2 a), which I will now de- 

 scribe, has the form of a little hook, having a 

 diameter of about 10 millim., with its two extre- 

 mities distant from each other by nearly the length 

 of a third of the circumference of the whorl. We 

 can distinguish in individuals of this age, besides 

 Nautiiu^Bohemicus, the body-chamber, another division of the shell 

 Barrande. which represents the air-chambers. Tlie crystal- 



"' ' ''growth!'^^^ ° line condition, however, of the hmestone prevents 

 us from recognizing in this second division the septa which without 



* The illustrations in the original form a lithographed plate (Taf. 1), fig. 1 of 

 which is the Theca noticed at p. 6 of Journ. No. 38, Miscell. The remaining 

 figures are here reproduced as woodcuts, and retain their original nuuil)ering for 

 the sake of uniformity of reference. — Transl. 



VOL. X. — PART II. E 



