FORMATIONS AND FOSSILS OF SOUTH MANCHURIA 73 



peitouitzense Grabau. Kobayashi's specimen may agree with Grabau's 

 second specimen. One of my specimens is 30 mm long and is very 

 slightly enlarged from the base to the top. The cross section of 

 the conch apparently was circular. The siphuncle is located some- 

 what excentrically. Three camerae occupy a length equal to the 

 diameter of the conch, and three annulations occur in the same 

 length. Where the diameter of the conch is 7 mm, the concavity of 

 the septa equals 1.5 mm. The maximum diameter of the siphuncle 

 here is estimated as 1.5 mm, and the height of camerae averages 

 2.2 mm. The deposition of the calcareous matrix in the camerae is 

 rather unusual. 



Formation and locality. — ^Middle Ordovician, Ssuyen formation: 

 Upper and lower fossil horizons of the black banded limestone beds, 

 near the Mu-hsin-tai colliery, Liao-tung, Manchuria. 



Plesiotype.—\J.^:^M. No. 83694. 



Genus SPYROCERAS Hyatt, 1879 



SPYROCERAS species undetermined 



Plate 38, Figube 5 



One specimen of SpyroGeras (U.S.N.M. No. 83695) occurs in Lou- 

 derback's collection from central China. It is 67 mm long and con- 

 sists of the living chamber only, no trace of the camerae being left. 

 It enlarges from a dianieter 22.5 mm at the base to 26.5 mm at a point 

 47 mm farther up ; thus an apical angle is very low. The cross sec- 

 tion of the conch is circular. The crests of five annulations occur 

 in a length equal to the diameter of the conch. They show some sig- 

 moid curvature on the lateral surfaces of the conch. These annula- 

 tions are about two-thirds of a millimeter in height, are rather 

 broadly rounded, and are separated by intermediate grooves of about 

 the same width. The surface of the conch is ornamented by very 

 faint vertical striae which cross the annulations. This specimen 

 seems to belong to a new species, but as no trace of the camerae is 

 preserved I hesitate to give a new specific name to the fragment. 



Formation and locality. — Upper Ordovician, near Han-chung-fu, 

 Shensi, China. 



Genus PLECTOCERAS Hyatt, 1884 

 PLECTOCERAS OHTAEAI, new species 



Plate 24 



One of my students, the late Chujiro Ohtaka, collected near Pen- 

 hsi-hu, during a geological excursion of the Manchurian Teachers' 

 College, a large but broken cast of a coiled cephalopod. Though 

 this specimen is rather fragmentary and only a mold, it became 

 clear, after making a plaster cast and carefully examining it, that it 



