MOLLUSCGA. 827 
Orthoceratites Breyn. Shell elongato-conical, straight, poly- 
thalamous, with septa perforated by siphon middle or subcentral. 
(Straight, not spiral Nautili.) 
Sp. Orthoceratites regularis SoutotH., Bronn Leth. geogn. Tab. I. fig. 10, in 
Thonschieferkalk (Wenlock shale?) 
Gen. Actinoceras BRONN does not, according to QUENSTEDT, differ from 
Orthoceratites. 
Appendix to the Nautilacea. Family of Ammonitacea. Shell 
polythalamous, with siphon external, marginal. Septa at the margin 
lobate, sinuate. 
Cornu Ammonis. These petrifactions are of various, some of very re- 
markable, size. If the animal was placed, as we may conclude from analogy, 
within the shell as Nautilus is, the siphon would lie on the ventral side 
towards the margin of the funnel, and the expression Sipho dorsalis, used 
by Palzontologists, is consequently incorrect.—A mmonites are met with in 
great numbers, especially in the transition and older secondary formations, 
In the lowest chalk-strata they are still numerous, but afterwards decrease 
rapidly and after the chalk-periods are met with no more on our earth. 
Compare G. Dr Haan Specimen inaug. exhibens Monographiam Ammo- 
niteorum et Goniatiteorum, L. B. 1825, 8vo; L. De Bucu Note sur les 
Ammonites, Ann. des Sc. nat. XVII. 1829, pp. 267—275; Sur la distribution 
des Ammonites en familles, Ann. des Sc. nat. Xv1II. 1829, pp. 417—426; 
Ueber Ammoniten, tiber ihre Sonderung in Familien, &c., Physik. Abhandl. 
der Berliner Akad. d. Wissensch., aus dem Jahre 1830; Ueber Ceratiten, 
ibid., a. d. J. 1848; F. A. Qurnstept Die Cephalopoden, Nebst einem 
Atlas von 36 Tafeln. ‘'Tiibingen, 1849, 8vo. 
Ammonites BREYN. Shell spiral, discoidal. 
Sub-genera: Goniatites Dr Haan, Ceratites ejusd. and some 
others seem only to form sections, with species passing from one 
section into another. 
Sp. Ammonites nodosus Brua., Ceratites nodosus Dk Haan, Bronn Leth. 
geogn. Tab. Xi. fig. 20; V. Bucn Ueb. Ceratiten, Tab. 1. 1. fig. 1, from the 
Muschelkalk. The species of the section of Gonatites are found in the 
transition formations. 
Scaphites PARKINSON. 
Hamites Sowerey. Shell incurved at the apex, produced into 
a straight tube. 
Sp. Hamites rotundus SowERBY, BRONN Leth. geogn. Tab, XXXII. fig. 9, from 
the chalk-formations. 
Turrulites Montr., Lam., Zwrrites De HaAAn. 
