70 BULLETIIT 164, UNITED STATES NATIONAL MUSEUM 



8°. The cross section of the conch has been somewhat compressed 

 laterally by rock pressure. The siphuncle is located ventrally, its 

 center being 5.2 mm from the wall of the conch near the top. Five 

 and five-tenths annulations occur in a length equal to the diameter of 

 the conch. "Where the dorsoventral diameter of the conch is 13 mm, 

 that at its passage through the septa appears to have been 2.7 mm, 

 but seems not to enlarge within the camerae. The concavity of the 

 septa equals 2.2 mm, and height of its camerae is 3.2 mm. The septal 

 neck is rather short, about 1 mm or less in length. The annulations 

 are 2 mm wide, rather low, and 3.1 mm apart from crest to crest. 

 These annulations are nearly transverse along the dorsal side of the 

 specimen and along the median part of the opposite side, but run 

 obliquely along the lateral sides at a rather low angle. 



The specific name is given in honor of Dr. George D. Louderback, 

 of the University of California, who collected this and many other 

 fine specimens in central China. 



Comparisons. — This species may be compared with Cycloceras 

 arcuoliratum (Hall) from the Trenton and Black River formations 

 of the United States, but has more rounded and broader annulations 

 and less obliquity of those on the lateral sides of the specimen. 



Formation and locality. — Upper Ordovician : Near Han-chung-fu, 

 Shensi, China. 



^oZo^ype.— U.S.N.M. No. 83690. 



CTCLOCERAS AOKII, new species 

 Plate 14, FiGtrEB 7 



Description. — The specimen is 60 mm long and has a rather low 

 apical angle. The cross section of the conch may be slightly de- 

 pressed, while that of the siphuncle is circular. Four annulations 

 occur in a length equal to the diameter of the conch. The number of 

 camerae in an equal length is six. The concavity of the septa is esti- 

 mated at 3 mm. The center of the siphuncle is located 5.5 mm from 

 the ventral wall of the conch. At the middle of the specimen, the 

 diameter of the siphuncle at its passage through the septa is 1.2 mm, 

 enlarging to 1.8 mm within the camerae. The annulations are 3 mm 

 wide, about 1 mm in height, and 5 mm apart from crest to crest. The 

 annulations run obliquely along the lateral sides at an angle of about 

 5°. The interior of the camerae is entirely filled with calcareous 

 matrix, while that of the siphuncle is rather empty. 



The specific name is given in honor of Prof. R. Aoki, of the Tohoku 

 Imperial University in Japan. 



Comparisons. — As is seen from the above description, this species 

 is very closely allied to Cycloceras manchuriense, but differs in having 

 a comparatively slender and rather unnummuloidal siphuncle in con- 



