FOSSILS OF THE DEVONIAN. 



201 



fragment 45 mm in diameter, preserving three air-chambers, that is closely 

 related to this form; the concavity of the septa is much greater, being 15 mm . 

 In some respects these fragments are allied to Orthoceras Bebryx Hall 

 (Pal. N. Y., vol. v, pt. 2, p. 275), of the Hamilton and Chemung Groups of 

 New York, but appear to belong to a distinct species. 



II. This is a more slender form than the preceding, and diminishes less 

 rapidly in receding from the chamber of habitation. Transverse section 

 circular. Apical angle, 5 to 6. Chamber of habitation large, without any 

 constriction as far as observed. Air-chambers numerous, having a depth of 

 3 mm where the diameter of the tube is 13 mm . Septa thin, the concavity 

 equal to a little less than the interspaces. Sutures transverse, straight. 



The best preserved specimen is 60 mm in length, with a diameter at the 

 septate end of ll mm , near the mouth of the chamber of habitation of 16 mm , 

 the chamber of habitation having a length of 35 mm . Surface characters un- 

 known. This form is related to Orthoceras exile Hall (Pal. N. Y., vol. v, 

 pt. 2, p. 290), of the Hamilton Group of New York. 



III. This fragment has three septa in a length of 25 mm ; transverse sec- 

 tion slightly ovate, as 8 to 9 ; greatest diameter, 27 mm . Apical angle about 5. 

 Septa thin, with a concavity equal to the depth of the chambers Siphuncle 

 eccentric, distant from the nearest point on the walls of the air-chambers 

 about two-fifths the greatest diameter of the tube. The "diameter at the 

 septa is 2 mm , where the major diameter of the tube is 18 mm . 



The greater depth of the air-chambers and the eccentric position of the 

 siphuncle distinguish this from the preceding form. 



IV. Several small fragments of an annulated species occur that are not 

 unlike portions of small specimens of Ortlioceras Thoas Hall (Pal. N. Y., vol. 

 v, pt. 2, p. 261), of the Upper Helderberg Group. A specimen 7 mm in 

 diameter has seven annulations in a distance of 21 mm . Septa and siphuncle 

 not observed. 



V. Large annulated form, 30 mm in diameter. Annulations narrow, de- 

 pressed, with a broad, slightly-depressed area between them, five annula- 

 tions in a distance of 30 mm . The margins of the septa appear about midway 

 between the annotations. 



