82 BULLETIN 16 4, UNITED STATES NATIONAL MUSEUM 



ring, which feature also distinguishes Kobayashi's specimen from 

 Grabau's Actinoceras tani. 



Foniiation and locality. — Middle Ordovician, Ssuyen formation: 

 Lower fossil horizon of the black banded limestone beds, just north 

 of and 4 to 5 miles southwest of the Pen-hsi-hu colliery Liao-tung, 

 Manchuria. 



Cotypes.—V.^.'^M. Nos. 83708 and 83709. 



ARMENOCERAS BASSLERI, new species 



Plate 22, Figuees 5, 6; Plate 40, Figxjee 12 



Description. — The holotype is 85 mm long, enlarging laterally 

 from a diameter of 29 mm to 39 mm in a length of 46.5 mm, indi- 

 cating an apical angle of about 16°. The cross section of the conch 

 is somewhat depressed, while that of the siphuncle is circular. The 

 siphuncle is about central in its position; its diameter is estimated 

 at 13 mm at the middle and its center is located 8 mm from the 

 ventral wall of the conch. Nine camerae occupy a length equal to 

 the diameter of the conch. Where the lateral diameter of the conch 

 is 36.5 mm the concavity of the conch equals 7 mm. Near the lateral 

 margins of the conch the sutures of the septa are shown as having 

 a very slight sigmoidal shape, and the septa come into contact with 

 the lower side of the segments of the siphuncle near its inner mar- 

 gins, but the underlying connecting rings are not so distinctly adnate 

 to the septa. The interior of the siphuncle is occupied by calcareous 

 matrix, leaving a comparatively large endosiphuncular passage, and 

 its narrow diverticula into the lateral margins of the segments of 

 the siphuncle. The septa are thickened regularly by calcareous mat- 

 rix, which occurs both on the upper and under sides of the septum, 

 leaving narrow, diagonal, and saucerlike spaces in the middle of 

 each camera but just outside of the segments of the siphuncle. 



Living chamber and outer surface of the shell unknown. 



The specific name is given in honor of Dr. R. S. Bassler, head 

 curator of geology of the United States National Museum, from 

 whom I have received much assistance in this work. 



CompaHson. — This species differs from all described oriental 

 species of Armenoceras in having a very large ratio of the diameter 

 of the siphuncle to that of the conch, and slightly sigmoidal shape 

 of the sutures. 



Formation and locality. — Middle Ordovician, Ssuyen formation: 

 Lower fossil horizon of the black banded limestone, near Hsia-kang- 

 yao, 3.5 miles southeast of the Yen-tai colliery, Liao-tung Manchuria. 



Holotype.— \^.'^:^M. No. 83759. 



