FORMATIOlSrS AND FOSSILS OP SOUTH MANCHIIIIIA 85 



forward. The septa of the lower part of the specimen are thickened 

 by deposition of calareous matrix. 



A second specimen (pi. 15, fig. 1), consisting of a siphuncle 177 

 mm long, enlarges from a lateral diameter of 27 mm at its base to 

 31 mm near the top. This specimen shows very distinctly the con- 

 necting portion between the septal necks and the rings, a character- 

 istic feature of Armenoceras. 



A third specimen (pi. 15, fig. 3), also a siphuncle, is 123 mm long. 

 The enlargement of this specimen is peculiar; at its apical part it 

 enlarges at an angle of 20° from the lateral diameter of 12 mm at 

 the base to 29 mm at a point 41 mm farther up. From this point it 

 enlarges in diameter very gradually to the top. 



Formation and localities. — Middle Ordovician, Ssuyen formation : 

 Lower fossil horizon of the black banded limestone beds near the 

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



Holotype and paratypes.—U.S.^M. Nos. 83703 and 83704. 



ARMENOCERAS ELONGATUM, new species 



Plate 17, Figtjkes 1-4; Plate 18, Figtjeb 8 



Description. — The holotype, 96 mm long, has a lateral diameter 

 increasing from 15 mm near the base to 33 mm near the top, the 

 apical angle being 8°. The cross section of the conch is apparently 

 circular near the base and elliptical laterally near the top; that of 

 the siphuncle is circular throughout, but only the dorsal half of 

 the specimen remains, the ventral half having weathered away near 

 the base, while almost the whole of the dorsal portion remains near 

 the top. Ten camerae occupy a length equal to the lateral diameter 

 of the conch. The siphuncle is 7.5 mm in diameter near the base 

 of the specimen and 10.5 mm at its middle, the ratio of its diameter 

 to that of the conch varying between 21 : 50 and 25 : 50 within the 

 43 mm length of the specimen. The distance between the siphuncle 

 and the ventral side of the conch is about 4 mm near the base and 

 2.5 mm near the top. The concavity of the septa varies from 4.5 mm 

 to 5 mm. Where the lateral diameter of the siphuncle is 10.5 mm, 

 that of the passage of the siphuncle through the septum is 6 mm. The 

 inner margin of the septa, at the passage of the siphuncle through 

 the septa, curves faintly downward, but does not form a septal neck. 

 The interior of the siphuncle and almost all the septal interspaces of 

 the ventral side are filled with typical actinoceroid deposits of 

 calcareous material, leaving the usual central endosiphuncular pas- 

 sage and its diverticula into the outer margin of the connecting rings. 



Living chamber of the shell unknown. Outer surface apparently 

 smooth. The cross section near the top of a second specimen is ex- 

 actly the same as the first. The dorsoventral diameter of the conch 



