80 BULLETIN 16 4, UNITED STATES NATIONAL MUSEUM 



Genus ARMENOCERAS Foerste, 1924 



ARMENOCERAS ORIENTALE, new species 



Plate 16, Figure 9 ; Plate 40, Fiquke 14 



Description. — A large, well-preserved specimen, retaining all the 

 living chamber, becomes the holotype of another new species. It is 

 311 mm long, 124 mm of which belongs to the living chamber. Its 

 lateral diameter enlarges from 31 mm near the base to 72.5 mm at 

 a point 245 mm farther up, the apical angle being about 7°. The 

 cross sections of the conch and the siphuncle apparently are depressed, 

 but only the dorsal half of the specimen remains, the ventral half 

 having weathered away. The siphuncle is located ventrally, its 

 center being 14 mm from the dorsal wall of the conch at a point 

 50 mm above the base. The siphuncle is 12.2 mm in diameter near 

 the base and 15.5 mm at a point 61 mm above, the ratio of its diameter 

 to that of the conch being 8 : 25. The number of camerae in a length 

 equal to the lateral diameter of the conch is 16.2. The concavity of 

 the septa varies from 8.5 mm near the base of the specimen to 14.5 

 mm at the top of its camerae. The length of the camerae varies 

 from 6.5 mm at the oldest to 4.1 mm at the youngest. Where the 

 lateral diameter of the siphuncle is 13.2 mm that of the passage of 

 the siphuncle through the septum is 7.5 mm. Between the connecting 

 rings this septum is horizontal, and the inner margin of the septum 

 extends about 3 mm inward from the vertical projection of the outer 

 margin of the septal rings. These rings are in contact with the septa 

 both above and below for a radial width of 2 mm. In the interior 

 of the siphuncle nearly the whole space of the central part is filled 

 with the calcareous matrix, leaving comparatively broad empty spaces 

 in the portion of the marginal nummuloids. The shell and some 

 septa are slightly and very irregularly thickened by calcareous 

 matrix. Surface of the shell unknown. 



Goviparisons. — This very complete specimen differs from all other 

 described oriental species in having a comparatively small apical 

 angle and highly nummuloidal segments of the siphuncle, and the 

 horizontal inner margin of the septa between the connecting rings. 

 I am not acquainted with any American or European species with 

 which this species is likely to be confounded. 



Formation am,d locality. — Middle Ordovician, Ssuyen formation: 

 In the lower fossil horizon of the dark gray limestone beds, near 

 Hsia-kang-yao, 3.5 miles southeast of the Yen-tai colliery, Liao-tung, 

 Manchuria. 



Holotype.— [J.^.'^M. No. 83707. 



