rORMATIONS AND FOSSILS OP SOUTH MANCHUBIA 79 



Genus NYBYOCERAS Troedsson, 1926 



NYBYOCEEAS FOERSTEI Endo 



Plate 25, Figures 3-5 ; Plate 26, Figtibes 9, 10 



1930. Nytyoceras foerstei Endo, Denison Univ. Bull., Journ, Sci. Lab., vol. 25, 

 p. 298, pi. 60, figs. 1 a-c. 



Description. — The holotype is 127 mm long, and its apical angle 

 seems to be rather small. The cross section of the conch is somewhat 

 depressed, while that of the siphuncle is circular, a part of the dorsal 

 side of the conch having weathered away. The dorsoventral diameter 

 of the conch at the top of the specimen is estimated as about 57 mm, 

 while its lateral diameter is about 63 mm. The number of camerae 

 in a length equal to the lateral diameter of the conch is seven. The 

 diameter of siphuncle at the top of the specimen is 21 mm. The 

 ratio between the diameter of the siphuncle and the dorsoventral 

 diameter of the conch is 37 : 100. The distance of the siphuncle from 

 the ventral wall of the conch at the top of specimen is 3 mm. Siphun- 

 cle is strongly nummuloidal, and its anterior is filled with actino- 

 ceroid deposits of calcareous material, leaving a central endosi]3hun- 

 cular passage. Septal neck rather conspicuous. On the dorsal side 

 of the conch the septa are in contact with the segments of the siphun- 

 cle below instead of those above, but ventrally they are conspicuously 

 in contact with the segments above, and laterally the same form of 

 contact predominates. It was upon this very characteristic struc- 

 ture that Troedsson established the subgenus Nyhyoceras^ which I 

 have raised to generic rank. Both sides of the septa on the dorsal 

 side of the conch are covered by a deposit of calcareous mate- 

 rial, and the interior of the camerae on its vertical side is almost 

 filled by a similar deposit. The sutures of the septa are very oblique, 

 the surface of the shell apparently smooth. 



The specific name is given in honor of Dr. August F. Foerste, of 

 Dayton, Ohio, from whom I have received valuable help and many 

 suggestions in my study of the Manchurian Ordovician fossils. 



Gomparisons. — This species is readily distinguishable from Ny- 

 hyoceras hekkeri Troedsson from the Lyckholm bed (Fi) at Nyby, 

 Estonia, in having a siphuncle of relatively smaller diameter and 

 shorter camerae. 



Formation and locality. — ^Lower Ordovician, Wuting formation: 

 In the black banded limestones near San-tao-kang-tzu, 1.5 miles 

 north of the Pen-hsi-hu colliery, Liao-tung, Manchuria. 



Eolotype.—V.S.'^.'K. No. 83455. 



