100 BULLETIN 1G4, UNITED STATES NATIONAL MUSEUM 



rather considerable width in the area immediately surrounding the 

 passage of the siphuncle through the septa; also the slightly down- 

 ward curving of the margin of the septa and the absence of a dis- 

 tinct septal neck show that this species belongs distinctly to Ai'me- 

 noceras. The siphuncle is rather excentric. The inside of the 

 siphuncle is filled with a calcareous deposit, leaving only the endo- 

 siphuncular passage and its diverticula. The calcareous deposits in 

 the camerae are irregular. 



Formation aiid locality. — Middle Ordovician, Ssuyen formation: 

 Lower fossil horizon of the black banded limestone beds, 4 to 5 

 miles southwest of the Pen-hsi-hu colliery. Another fragmental 

 specimen of this species came from the same horizon, near the Wu- 

 hu-tsui colliery, Liao-tung, Manchuria. 



Plesioty'pes.—\5.^:^M.. Nos. 83737 and 83738. 



ARMENOCERAS TABEI, new species 



Plate 21, Figures 8, 9 



Description. — The holotype is 70 mm long, enlarging slightly 

 from the base to the top. The cross section of the siphuncle is cir- 

 cular, while that of the conch apparently is depressed a little, but 

 only the lateral half of the conch remains; 6.3 and 5.5 camerae, 

 respectively, occupy a length equal to the lateral and dorsoventral 

 diameters of the conch. The siphuncle is 13.5 mm in diameter at the 

 middle of the specimen, the ratio of its diameter to the dorsoventral 

 diameter of the conch being 31 : 100. The siphuncle is located com- 

 paratively ventral of the center of the conch; the distance between 

 the siphuncle and the ventral side of the conch is 12 mm at the middle 

 of the specimen. The concavity of the septa averages 15.5 mm. 

 The siphuncle is strongly annulated where the diameter of the 

 siphuncle is 13.5 mm, that of the passage of the siphuncle through 

 the septum is 6 mm. Between the connecting rings this septum is 

 horizontal, and the rings are in contact with the septa both above 

 and below for an average radial width of 3.5 mm. The interior of 

 the siphuncle is filled with calcareous material, leaving the usual 

 central endosiphuncular passage. Both sides of the septa also are 

 thickened with calcareous deposits. The surface of the shell is 

 apparently smooth. Living chamber unknown. 



The specific name is given in honor of Prof. H. Yabe, of the 

 Tohoku Imperial University in Japan. 



Formation and locality. — Middle Ordovician, Ssuyen formation: 

 a grayish black limestone bowlder believed to have come from the 

 Ssuyen formation, collected in river drift at the Niu-hsin-tai colliery, 

 Lifio-tung, Manchuria. 



Eolotyfe.—\i.^:^M.. No. 83739. 



