FORMATIONS AND FOSSILS OF SOUTH MANCHUillA 67 



camerae occupy a length equal to the diameter of the conch. Where 

 the diameter of the conch is 11.6 mm, the diameter of the giphuncle 

 is estimated at 1.4 mm. The septae are straight transversally or 

 slightly convex toward the apical part, which is a very characteristic 

 feature. Septal distance is very great, being estimated as between 

 3 mm and 7.5 mm. Surface of the shell is slightly annulated. In- 

 teriors of the siphuncle and camerae are filled almost entirely with 

 a calcareous matrix. 



This species is characterized by having straight septae, large 

 septal distances, and a slightly annulated surface. 



Formation and locality. — ^Lower Ordovician, Wuting formation: 

 In the gray limestone, near Ta-wan-kou, 1.5 miles northeast of the 

 Niu-hsin-tai colliery, Liao-tung, Manchuria. 



Holotype.—\]S.'^M. No. 83684. 



ORTHOCERAS TOYAMAI, new species 



Plate 13, Figukes 4, 5, 13; Plate 40, Figxtbe 17 



Description. — The holotype is 74 mm long, enlarging slightly 

 from a diameter of 11 mm at the base to 17 mm at the top. The 

 number of camerae in a length equal to the diameter of the conch 

 equals three at the middle part. The cross sections of the conch 

 and the siphuncle are almost circular, or slightly depressed, but the 

 dorsal part of the shell has been weathered away, leaving some 

 doubt on this point. The siphuncle is central in location, rather 

 tubular, but slightly enlarged within the camerae. Where the diam- 

 eter of the specimen is 13 mm, and where the septae are 4.5 mm 

 apart, one of the segments of the siphuncle has a diameter of 2.5 mm 

 at mid height, and the passage of siphuncle through the septum is 

 1.5 mm. The concavity of the septae is relatively small. The 

 deposition of the calcareous matrix in the siphuncle and camerae 

 is very irregular; in some parts it fills completely the whole space 

 of the siphuncle and the camerae while in other places these are 

 rather empty. The surface of the shell is very slightly annulated 

 so far as seen in the polished longitudinal section. 



A second specimen, 61 mm long, enlarges from a diameter of 13 mm 

 at the base to 17 mm at a point 36 mm farther up. The concavity of 

 the septae is 2.5 mm and the septae average 4.5 mm apart. The 

 cross section of the conch is somewhat depressed. 



A third specimen from Pen-hsi-hu is 46 mm long. The concavity 

 of the septae is 2.5 mm, and they average 6 mm apart. The enlarg- 

 ing of the segments of the siphuncle within the camerae is rather 

 clear, but, on the contrary, the annulation of the surface of the 

 shell is very faint. 



