FORMATIONS AND FOSSILS OF SOUTH MANCHURIA 93 



septum at an acute angle ; a similar acute angle is shown where the 

 immediately overlying connecting rings meet the same septum; this 

 structure is characteristic of Armenoceras. The calcareous matrix 

 is rather slightly developed on the anterior margin of the septa 

 in the younger part of the shell, while comparatively much greater 

 quantities are found in the camerae at the older part of the shell. 



A second specimen from near the Pen-hsi-hu colliery (pi. 18. 

 fig. 5) is 40 mm long. The ratio between the diameter of the 

 siphuncle and that of the conch is 3 : 10. 



Formation and locality. — Middle Ordovician, Ssuyen formation: 

 Lower fossil horizon of the black banded limestone, near the Niu- 

 hsin-tai and the Pen-hsi-hu collieries, Liao-tung, Manchuria. 



PU^otypes.—{]S.'^M. Nos. 83726 and 83727. 



ARMENOCERAS NANUM TAKAYAMAI, new variety 



Plate 16, Figtjrjes 7, 8 



Description. — Another fragmentary specimen, 17.5 mm long, has a 

 rather cylindrical conch, enlarging very slightly from the base to the 

 top. The cross section of the conch apparently was slightly 

 depressed ; the siphuncle is practically central. The lateral diameter 

 of the conch at the top is estimated as 8 mm, while that of the si- 

 phuncle is 2 mm. The number of camerae in a length equal to the 

 diameter of the conch is 6.2. The convexity of the septa at the 

 middle part of the specimen is 2 mm; the length of the camerae 

 averages 1.5 mm. The inner margin of each septum is connected 

 with both the upper and lower connecting rings at an acute angle. 

 The interior of the siphuncle is filled with calcareous matrix, leav- 

 ing a narrow endosiphuncular passage. The septa are somewhat 

 thickened by the calcareous matrix which occurs on both the upper 

 and lower sides of the septum. 



A second specimen from Wu-hu-tsui district (pi. 16, fig. 7) is 

 51 mm long. Though the manner of depositing the calcareous 

 matrix is very irregular, other general features closely agree witji 

 that of the first specimen. Six camerae occupy a length equal to 

 the diameter of the conch. The height of the camerae is estimated 

 to average 2 mm, and the concavity of the septa at the lower part of 

 the specimen is 2.5 mm. This variety differs from the type species 

 in having a rather cylindrical conch, shallower concavity of the sep- 

 tum, and comparatively longer septal distance. 



The name of this variety is given in honor of Y. Takayama, who 

 collected the holotype. 



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

 Lower fossil horizon of the black banded limestone at Tou-f ang-kou, 

 101621—32 1 



