32 



rows. There are fourteen nodes on each transverse ridge, in the 

 specimen, and hence, there are fourteen longitudinal rows of nodes. 

 A longitudinal line crosses each furrow from node to node, but 

 it is nearly obsolete at the bottom of the furrows. The width of 

 a furrow or distance between two nodes, at the larger end is 

 equal to one-third of the shorter diameter of the shell; but, at 

 the smaller end of the specimen, the distance between two nodes 

 is more than one-third of the greater diameter. The width of the 

 annulatinus, therefore, do not bear a regular proportion to the 

 diameter of the shell. There is an obscure node between the 

 regular nodes, at the larger end, but none near the smaller end. 

 The septum shown, at the smaller end, is highly arched, and, it 

 appears as if there is only one septum to correspond with each 

 annulation. The shell is thick, and the outer surface of the fur- 

 rows shows no lamellose lines of growth, but, possibly, a better 

 preserved specimen would show such lines. 



This species has more resemblance to O. nodocosium, from the 

 Niagara Group, than to any other described species. O. nodocos- 

 tum is frequently classed as a synonym for O. annulatum, but 

 the two species are distinct and are readily distinguished, by any 

 palaeontologist, from an examination of the shells or the caste. 

 The annulations are wider and the nodes are not as prominent, 

 in this species as they are in O. nodocostum, and the septa are 

 evidently more distant from each other, and more highly arched. 

 Orthoceras was a pelagic shell and, probably, lived as long upon 

 the face of the earth as any other genus ever did. The annulated 

 forms made their appearance, in the Lower Silurian age, and are 

 found in all Groups of rocks, from there into the Subcarbonifer- 

 ous. The form called O. annulatum occurs, in the Niagara Group, 

 on both sides of the Atlantic, and almost everywhere, that the 

 rocks of that age are known to exist. 



Found by James G. Caldwell, in whose honor the specific name 

 is given, in the Upper Helderberg Group, in Clarke County, Ind- 

 iana, and is now in the collection of Wm. F. E. Gurley. 



Family GOMPHOCERATIM1. 



POTERIOCEEAS JERSEYENSE, n. sp. 



Plate IV, Fig. 3, side view of a specimen somewhat compressed. 



Shell large, acutely obovate or balloon-shaped. Body chamber 

 much longer than the septate . portion. Greater diameter about 



