10 SYNOPSIS OF THE CHARACTERS OF THE 



Cycloceras annulare. Flem. sp. 



Ortliocera annularis. Flem. An. Phil. 

 Sp. Ch. — Cylindrical, girt with numerous, distant, even transverse rings or ridges, surface smootli. 

 This beautiful little species is usually found in fragments about an inch in length, and quarter of an inch 

 in diameter; there are usually about two chambers between two of the external rings. 



Cycloceras l^vigatum. M'Coy. (PI. I. fig. 3). 



Sp. Ch. — Very gradually tapering, regularly girt with equal rounded rings very slightly oblique, rather 

 more than their own thickness apart, surface smooth. 



This species belongs to the very interesting but difBcult division of the Orthoceratites, to which, from the 

 prominent ring-like elevations on the surface, I have given the name of Cycloceras; tlie present species is closely 

 allied to the O. Ibex (of Sow. not of Phil.), and to the O. annulatiis of Heisinger (not of the Min. Conch.) It 

 is most likely to be confounded with the O. lineolatmn, Phil. (O. annidatum of the Geol. York) from which 

 it is distinguished by its perfectly smooth surface. A specimen one inch three lines in length, and nine lines in 

 diameter, does not taper more than lialf a line. 



Cycloceras lineolatum. Phil sp. 



Orthoceras lineolatum. — Phil. Pal. Fos. — Orthoceras annnlatum. — Phil. Geol. York. (Not of tlie Min. Con.) 



Sp. Ch. — Very gradually tapering ; surface with numerous rounded oblique rings, the intervening spaces 

 with fine, obtuse, slightly waving transverse striae. 



I have only seen one flattened fragment of this rare species. 



POTERIOCERAS. M' Coij . 



Gen. Ch. — Sliell fusiforme, short; mouth contracted ; siphuncle dilated between the chambers, excentric. 

 Distinguished from the true Orthoceratites by its short, fusiform contour, and contracted mouth. 

 Mr. Sowerby proposed the name Gomphoceras for a fusiform species of the Silurian rocks, but that is a 

 well known genus of Insects. 



POTERIOCERAS FUSIFORME. SoW. SP. 



Orthocera fusiformis. Soie. Min. Con. Ortboceras fusiforme. Phil. Geol. Ycjrk. 



Sp. Ch. — Elongate, fusiform ; length three times the width ; siphuncle excentric towards the dorsal side. 



This elegant species is distinguished from all others of the genus by its more elongate form, a specimen 

 six inches long only measuring one inch seven lines In the widest part. In tlie same specimen the mouth only 

 measured nine lines in diameter, the smaller end was six lines in diameter. 



POTERIOCERAS VENTRICOSUM. M'Coy. (PI. I. fig. 2). 



Sp. Ch. — Fusiform, width nearly half the length. 



This fine species is one of the largest of the fusiform group of Orthoceratites, to whicli I have given the ge- 

 neric name oi Poterioceras. It most nearly resembles the common P. fusiforme, but is easily distinguished by its 

 great proportional width ; the section is a very broad oval, siphuncle large, inflated, and sHghtly excentric. 

 Length of chambered portion figured three and a half inches, diameter of last chamber four and a half Inches, 

 diameter of thirteenth chamber from the last one inch four lines, septa three lines apart. 



