84 BULLETIN 16 4, UNITED STATES NATIONAL MUSEUM 



Description. — This plesiotype is 86 mm long, its lateral diameter 

 increasing slightly from the base to the top. As only the ventral 

 half of the specimen remains, the shape of the cross section of tlie 

 conch can not be exactly identified, but apparently is depressed later- 

 ally. Thirteen camerae occupy a length equal to the diameter of the 

 conch. The siphuncle is 16 mm in diameter at the upper part of 

 the specimen, the ratio of its diameter to that of the conch being 

 37:100. The siphuncle is located excentric in position. The con- 

 cavity of the septa averages 7 mm. Wliere the lateral diameter of 

 the siphuncle is 17.5 mm, that of the passage of the siphuncle through 

 the septum is 9 mm. Between the connecting rings this septum 

 curves gently downward but does not form a septal neck. This 

 inner margin extends about 4 mm inward from the vertical projec- 

 tion of the outer margin of the septal rings. These rings are in 

 contact both above and below with the septa for a radial width of 

 2.5 mm, which structures are characteristic features of Armenoceras. 

 The interior of the siphuncle is almost filled with calcareous matrix. 

 The septa are thickened very irregularly with the deposition of the 

 calcareous matrix, which appears as if it were deposited on both 

 sides of the septum. 



Formation and locality. — Middle Ordovician, Ssuyen formation: 

 The lower fossil horizon of the black banded limestones, just south 

 of the Wu-hu-tsui colliery, Liao-tung, Manchuria. 



Plesiotype.— U.S. l^.lsi. No. 83711. 



ARMENOCERAS ELEGANS, new species 



Plate 15, Figures 1-3 



One fragment of the conch and two large siphuncles of an Armen- 

 oceras constitute the material on which this new species is based. 



Description. — The first specimen (pi. 15, fig. 2), is 53 mm long and 

 enlarges laterally from 25 mm at the base to 45 mm at the point 25 

 mm farther up, so that the apical angle is rather large. The cross 

 section apparently is elliptical laterally, but only the ventral half 

 of the specimen remains. About nine camerae occupy a length equal 

 to the diameter of the conch when the counting is completed. 

 The siphuncle is excentric in position, the distance between the siph- 

 uncle and ventral side of the conch is 5 mm at the base. The diameter 

 of the siphuncle is about the same throughout the specimen. Where 

 the diameter of the conch is 30 mm, that of the siphuncle at its pas- 

 sage through the septa is 12 mm, enlarging to 18.5 mm at mid height 

 within the camerae. The septal necks appear to be about 1.5 mm in 

 length. The interior of the siphuncle is filled with calcareous ma- 

 terial, leaving a rather large endosiphuncular passage and its nar- 

 row lateral diverticula, which bend backward at first and then curve 



