FORMATIONS AND FOSSILS OF SOUTH MANCHURIA 107 



Formation and locality. — Middle Ordovician, Ssuyen formation: 

 From the lower fossil horizon in the black banded limestone 2 miles 

 south of the Niu-hsin-tai colliery, Liao-tung, Manchuria. 



Holotype.—TJ.S.'^M. No. 83T52. 



ORMOCERAS TAITZUENSE, new species 



Plate 22, Figxire 7 ; Plate 40, Figtxre 4 



Description. — The holotype is 48 mm long, enlarging laterally 

 from a diameter of 15 mm near its base to 21.5 mm at its top, indi- 

 cating an apical angle of 9°. The cross sections of the conch and 

 the siphuncle are apparently circular, but only the ventral half 

 of the specimen remains, the dorsal half having weathered away. 



The siphuncle was somewhat excentric laterally. The number of 

 camerae in a length equal to the diameter of the conch is about 4.5. 

 Where the lateral diameter is 18 mm, the concavity of the septa 

 equals 2.5 mm. The form of the segments of the siphuncle is 

 globular, but is somewhat depressed vertically at the contacts be- 

 tween successive segments. Where the lateral diameter of the si- 

 phuncle is 5.5 mm, that of the passage of the siphuncle through the 

 septa is 2 mm. The septal necks are short, usually 0.5 mm or less 

 in length. The interior of the siphuncle is occupied by calcareous 

 deposits, comparatively small in quantity, very irregularly dis- 

 tributed, while in the camerae they are found in rather large 

 quantities. 



Comparison. — This species differs from Ormoceras taii mainly in 

 its circular cross section of the conch, shallower concavity of the 

 septa, and the number of camerae in a length equal to the diameter 

 of the conch. 



Formation and locality. — Middle Ordovician, Ssuyen formation: 

 A black limestone bowlder believed to have come from a part of the 

 Ssuyen formation collected in a river drift at the Mu-hsin-tai col- 

 liery, Liao-tung, Manchuria. 



Holotype.— {J.S.'^M. No. 83753. 



ORMOCERAS species undetermined 



Plate 22, Figuke 1-3 ; Plate 14, Figueb 5 ; Plate 16, Figtjbb 11 



The first of four specimens referred to Ormoceras (pi. 22, fig. 1) 

 is 27.5 mm long, with a diameter of 8.5 mm (U.S.N.M. No. 83755). 

 Five camerae occupy a length equal to a diameter of the conch. The 

 apical angle is very low. The conch apparently was circular. The 

 traces of the comparatively narrow siphuncle occur along the lower 

 half of the natural longitudinal weathered section. 



