86 BULLETIN 164, UNITED STATES NATIONAL MUSEUM 



in this section is about 21 mm, while the lateral diameter is 25^ mm. 

 The number of camerae in a length equal to the lateral diameter of 

 the conch equals nine. The diameter of the siphuncle in the same 

 section is 10.5 mm, the ratio between the diameter of the siphuncle 

 and the lateral diameter of the conch being 21 : 50. The distance of 

 the siphuncle from the ventral wall in the same section is 3 mm. The 

 dorsal part of the camerae in this second specimen is not filled with 

 the calcareous matrix. 



A vertical section of a third specimen has been cut in a dorsoven- 

 tral direction through the center of the siphuncle ; in this section, as 

 seen in Plate 17, Figure 2, the concavity of the septa of the ventral 

 side is very conspicuous as compared with that of the dorsal side. 



Gom'parisons. — This species may be compared with Armenoceras 

 {Actinoceras) suhmarginale (Grabau) from the Machiakou limestone 

 of the Kaiping basin. North China, but the comparatively narrow 

 siphuncle and its position serve readily to distinguish it. This 

 species is also closely allied to Armenoceras {Actinoceras) manchu- 

 rense (Kobayashi) but differs in having a faintly downward curving 

 inner margin of the septum at the passage of the siphuncle through 

 the septum, while that part of A. manchurense is more horizontal. 



Formation and locality. — Middle Ordovician, Ssuyen formation 

 (holotype from the lower fossil horizon) : In the black banded lime- 

 stone beds, which are widely distributed south of the Niu-hsin-tai 

 colliery, Liao-tung, Manchuria. Paratype from the same beds on 

 the small hill, just south of Kan-chia-tun in the Wu-hu-tsui coal 

 basin, Manchuria. The third specimen was collected from the upper 

 fossil horizon just north of the Niu-hsin-tai colliery. 



Holotype and paraty pes.— U.S. liiM. Nos. 83712-83714. 



ARMENOCERAS HATAI, new species 



Plate 18, Figures 1-3 



Description. — The holotype is 50 mm long, slightly enlarging 

 laterally from the base to the top. The cross sections of the conch 

 and siphuncle are circular. The siphuncle is excentric, its center 

 being located 6 mm from the ventral wall of the conch. Seven and 

 one-half camerae occupy a length equal to the diameter of the conch. 

 Where the diameter of the conch is 22.5 mm, the maximum diameter 

 of the siphuncle is estimated at 8.5 mm, making the ratio of the 

 lattef to the former 19:45. The concavity of the septa and the 

 height of the camerae are estimated to average 4.5 mm and 2.7 mm, 

 respectively. The segments of the siphuncle are strongly depressed 

 vertically both above and below, and the connecting rings are in 

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

 1 mm. The interiors of the siphuncle and the camerae are filled 



