492 Miss Agnes Crane — Recent and Fossil CejjJialopoda. 



in all parts of the woiid. These primitive types are, however, widely 

 divergent, comprising the Nautilus, the curved Gyrtoceras, the straight- 

 shelled Orthoceras and Endoceras, the club-shaped Gomphoceras, and 

 the simply-coiled Lituites. Some of these generic forms enjoyed a 

 very brief existence, and after becoming specifically numerous, died 

 out almost as suddenly as they appeared. The Orthoceratites were 

 certainly, among the mollusca, the giant rulers of those ancient seas, 

 and many attained large dimensions, measuring ten or twelve feet 

 in length. One American species, truly an Orthoceras Titan^ esti- 

 mated by Dr. J, S. Newberry as weighing " some tons," must have 

 fairly rivalled the fabled living " Kraken," endowed by the older 

 naturalists with the power of sinking a ship seized in the clutches 

 of their snake-like arms. Tlie shell of Orthoceras is straight, and the 

 septa of the vertical chambers, pierced by a nearly central siphuncle, 

 are simple at their edges, like those of Nautilus. The last chamber 

 seems comparatively small for the occupation of an animal capable 

 of sustaining and directing such an enormous shell, and it has been 

 suggested that the shell was internal as in the living cuttles and the 

 extinct Belemnites. This view, which is not generally entertained, 

 was considered by the late Dr. S. P. Woodward^ to be untenable on 

 the grounds that in some specimens the exterior colour-bands appear 

 to have been preserved on the outer surface of the shell, and thus 

 prove it to have occupied an external position. There were 260^ 

 species of Orthoceras in the Lower Silurian rocks, a number which 

 increased to 626 in the Upper Silurian seas, when the life-conditions 

 were very suitable. They declined rapidly in the succeeding Paleeo- 

 zoic epochs, and were represented only by fourteen dwarfed forms 

 in the Triassic deposits, the dawn of the great Secondary life-period 

 of geologic history. In the curved and elegant Gyrtoceras, the 

 increase from 90 specific forms in the Lower Silurian rocks to 299 in 

 the upper beds is even still more remarkable, and affords an idea of 

 the enormous duration of time that must have elapsed during the 

 deposition of that early fossiliferous series. Only one species of the 

 genus survived in the Permian era. 



In the coiled Goniatites of the Upper Silurian beds we have the 

 first indications of that ornamentation of the edges of the chambers, 

 which subsequently became such a marked and beautiful feature in 

 the numerous family of the Ammonites which ranged in Europe from 

 the Trias to the Chalk, and of which there are several hundred 

 known species. Some specimens found in the Carboniferous rocks 

 of India must have been contemporary with the Goniatites, a fact 

 that is not without interest when the theory of the evolution of the 

 class comes to be considered. Ammonites have also been obtained 

 from the Oolitic deposits in the passes of the Himalayas at a height 

 of over 16,000 feet above the level of the sea, and afford a striking 

 instance of variations in the physical configuration of the world, for 

 it is obvious that when they lived and died the Himalayas were not, 

 and similar palgeontological data prove that those snow-clad moun- 



1 State Eeports of the Geology of Ohio. — Paleontology, vol. i. p. 263. 



2 Manual of the Mollusca. 2nd edition, 1868. S. P. Woodward. 

 ^ Barrande, ibid. 



