FORMATION'S AND FOSSILS OF SOUTH MAliTCHTJEIA 69 



annulations occur in a length equal to the diameter of the conch, 

 the number of camerae in the same length being 8.5. The concavity 

 of the septa equals almost 3.6 mm. The center of the siphuncle is 

 located 5.5 mm from the ventral wall of the conch. At a point near 

 the base, the diameter of the siphuncle at its passage through the 

 septa appears to have been 2 mm, enlarging to 3.2 mm within the 

 camerae. The septal neck is very short. The annulations are 3 mm 

 wide, about 1 mm high, and 5 mm apart from crest to crest. These 

 annulations are nearly transverse along the dorsal side of the speci- 

 men and along the median part of the opposite side, but they run 

 obliquely along the lateral sides at a 5° to 6° angle. 



A second specimen (pi. 14, figs. 8, 9), 54 mm long, has an apical 

 angle of 8°. The diameter of the conch is 13.5 mm and that of 

 the siphuncle 2.5 mm near the base. A vertical section has been cut 

 in a lateral direction through the center of the siphuncle. Six 

 camerae occupy a length equal to the diameter of the conch, four 

 annulations occurring in the same length. The obliquity of the an- 

 nulation of the calcareous material in the camerae is comparatively 

 irregular; the posterior camerae are filled entirely with the calcare- 

 ous matrix, while in the younger camerae the deposit is only small. 



A third specimen (pi. 14, fig. 12) is 66 mm long, the diameter 

 of the conch being 18.5 mm and that of the siphuncle 2.5 mm near 

 the top. The number of camerae and annulations in a length equal 

 to the diameter of the conch is 8.2 and 5 mm, respectively. 



Since the surface of the shell of this species is not well preserved, 

 I can not decide exactly whether it belongs to Spyroceras or Gyclo- 

 ceras, and therefore it is assigned to Oycloceras only tentatively. 



G omparison. — I am not acquainted with any American or Euro- 

 pean species with which this species is likely to be confounded. 

 But it may have some characters in common with Oycloceras un- 

 dulostriatum (Hall) from the Trenton limestone of New York, 

 although the different obliquity of the annulations, the comparatively 

 larger distance between the crests of the annulations, and other 

 details serve easily to distinguish it. 



Formation and locality. — Middle Ordovician, Ssuyen formation: 

 The lower fossil horizon of the black banded limestone beds, just 

 north of the Pen-hsi-hu colliery, also in river drift at the Niu-hsin- 

 tai colliery, Manchuria. 



Holotype and paraty pes. — U.S. ^M. Nos. 83688 and 83689. 



CYCLOCERAS LOUDERBACKI, new species 



Plate 36, Figure 16 



Description. — Specimen is 40 mm long and enlarges dorsoventrally 

 from 9 mm at the base to 13.2 mm at the top, the apical angle being 



