284 



PALJSONTOLOGT. 



ceras, Adelphoceras, BatTimoceraSy Treti)ceras, and Bactrites. The plates 

 were published at previous dates. The preliminary portion discusses 

 the classification and grouping of the species of Orthoceras adopted and 

 published by the author (' Groupement des Orthoceres,' 1868). The 

 basis of this classification rests on the " short-coned " or *' long-coned '' 

 form of the shell, the subordinate groups being founded on the nature 

 of the external ornamentation, the form of the transverse section of the 

 shell, the position of the siphuncle, and other minor characters. A de- 

 scription of the general characters of the " short- coned " Orthocerata 

 follows, attention being directed to the general form of the shell, to the 

 limits and variations of the apical angle, to the initial extremity, trans- 

 verse section, body-chamber, air-chambers, aperture, and septa of the 

 shell, to the position, form, and constituent elements of the siphuncle, 

 to the thickness and ornamentation of the shell, to the relations of the 

 group with the short-coned species of Cyrtoceras and the long-coned 

 Orthocerata, and to the distribution of the group in Bohemia and else- 

 where. The next part (pp. 35-99) describes the species of the short- 

 coned group of Orthocerata in Bohemia, 65 species, all new, being 

 described. [Owing to the great number of new species described in 

 this work, it has not been thought advisable to give a list of the names.] 

 After a consideration of the general characters of the long-coned Ortho- 

 cerata, the author divides this section into 21 groups, and describes the 

 species belonging to these. A short section is devoted to the discussion 

 of the general characters of each group, and to the distribution of the 

 species of the group in time. In all 457 species of long-coned Ortho- 

 cerata from the Bohemian basin are described, almost all of them being 

 new (pp. 100-678). Under the section of the long-coned Orthocerata 

 are placed the subgenera Huronia (with no Bohemian species), Endo- 

 ceras (with three Bohemian species), and Gonioceras (with no Bohemian 

 representative). 



The second division (pp. 679-758) gives descriptions of those species 

 of Cephalopoda known to occur in countries outside Bohemia, but 

 figured in the previously published volume of plates. The forms in 

 question comprise: — 2 species of Orthoceras and 1 of Trochoceras from the 

 Devonian formation of Erance; 2 species of Orthoceras from Great 

 Britain ; 21 species of Orthoceras (including Endocer^as) from Sweden ; 



1 species of Orthoceras and 3 species of Endoceras from Russia ; 1 

 species of Orthoceras from the Silurian of Franconia, and 1 from the 

 Carboniferous of Belgium ; 1 species of Nautilus, 2 of Orthocetns, 2 of 

 Endoceras, and 1 of Trochoceras (?) from the Silurian of Newfoundland; 



2 species of Cyrtoceras, 14 of Orthoceras, 4 of Huronia, 3 of Endoceras, 

 and 1 of Orthoceras ? (Discosorus) from the Silurian deposits of Canada ; 

 and 4 species of Orthoceras, 2 of Endoceras, and 2 of Huronia from the 

 Silurian rocks of the United States. 



The third division (pp. 759-787) is a critical consideration of the 

 characters of the genus Orthoceras proper, and of the subgenera Huronia, 

 Emloceras, and Gonioceras. Under the amended genus Orthoceras the 

 author places the following genera — Actinoceras, Ormoceras, Conilites, 



