CEPHALOPODA. 315 



BACTRITES, Sandberger. 1841. 



The genus Bactrites was founded by Dr. Guido Sandberger in 1841, and its 

 principal characters indicated by him in Leonh. und Bronn's Jahrb., p. 240. 



In 1850 Drs. G. and F. Sandberger reproduced the definition of the genus, 

 with descriptions and figures of three species: B. carinatus, B. gracilis, and B. 

 subconicus, in their great work, Die Versteinerungen des Rheinischen Schichtensystems 

 in Nassau; p. 124, pi. 11, 12, 17. 



Since its first publication the genus has been recognized by other naturalists 

 in several countries of Europe, among whom are Prof. F. A. Bxemer, Dr. Giebel, 

 Dr. Ferd. B(HD, If. J. Barrande, Prof. Gustave Ladbe and others. 



Uutil the present time no notice of this genus has been published in 

 America. The number of species described from all the palaeozoic countries is 

 very limited, compared with the other allied genera. Only thirteen species 

 have been recognized. Two of these are from the Silurian of Bohemia and 

 Russia. Eleven species have been described from the Devonian of the Rhenish 

 Provinces and the Harz. In Bohemia, where Cephalopodous life reached its 

 maximum development, only one species has been indicated; and this is very 

 limited in its vertical distribution. Two forms have also been recognized in 

 the Triassic. 



The species here described is from the Marcellus shales, at the base of the 

 Hamilton group, and has only been observed among collections from a single 

 locality. As a whole, the genus seems to be essentially a Devonian form, and 

 very local and irregular in its vertical and geographical distribution. 



On account of the slight " dorsal lobe" of the suture lines, over the insertion 

 of the siphuncle in the septa, these forms have been considered as belonging 

 with the GoniatitidaB. In well preserved specimens, where the septal margins 

 are nearly entire, this bending of the sutures is very slight; and is not a proper 

 sinus in the septa, but is apparently a sinus in the chamber walls, made by the 

 exposure of the siphuncular tube. Many Gyroceras and Trociioceras show a 

 similar sinus in the septal sutures, where the siphuncle is submarginal. The 

 genus Orthoceras, as now constituted, admits of so great a range of variation 



