CEPHALOPODA. 



87 



LITUITES, Breynius. 

 Etym., lituus, a trumpet. 



Syn., Hortolus, Moutf. (whirls separate.) Trocholites, Conrad. 

 Ex., L. convolvans, Schl. L. lituus, Hisinger. 



Shell, discoidal ; whirls close, or separate ; last chamber produced in a 

 straight line ; siphuncle central. 



Fossil, 15 sp. Silurian, N. America, Europe. 



TROCHOCERAS, Barrande, 1848. 

 Ex., T. trochoides, Bar, 

 Shett t nautiloid, spiral, depressed. 

 Fossil, 16 sp. U. Silurian, Bohemia. 



Some of the species are nearly flat, and having the last chamber pro- 

 duced would formerly have been considered Lituites. 



Fig. 45. Clymenia striata, Munst.* Fig. 46. C. linearis, Munst. 



OLYMENIA, Munster, 1832. 

 Etym., clymene, a sea-nymph. 

 Syn. Endosiphonites, Ansted. Sub-clymenia, D'Orb. 

 Ex., C. striata, pi. II., fig. 16 (Mus. Tennant). 

 Shell, discoidal ; septa simple or slightly lobed ; siphuncle internal. 

 Fossil, 43 sp. Devonian, N. America, Europe. 



FAMILY II. ORTHOCERATIDJE. 



Shell, straight, curved, or discoidal ; body chamber small ; aperture con- 

 tracted, sometimes extremely narrow (figs. 40, 41) ; siphuncle complicated. 



It seems probable that the cephalopods of this family were not able to 

 withdraw themselves completely into their shells, like the pearly nautilus ; 

 this was certainly the case with some of them, as M. Barrande has stated, 

 for the siphonal aperture is almost isolated from the cephalic opening. The 

 shell appears to have been often less calcified, but connected with more vas- 

 cular parts than in the nautilus ; and the siphuncle often attains an enor- 

 mous development. In all this, there is nothing to suggest a doubt of their 

 being tetrabranchiate ; and the chevron-shaped coloured bands preserved on 

 the orthoceras anguliferus,\ sufficiently prove that the shell was essentially 

 external. 



* Fig. 45. Sutures of two species of Clymenia from Phillips' Pal. Fos., Devon- 

 shire. 



\ Figured by D'Archiac and Verneuil, Geol. Trans. 



