FOEMATIONS AND FOSSILS OF SOUTH MAISTCHUBIA 83 



ARMENOCERAS RESSERI, new species 



Plate 17, Figtjke 6 



Description. — The holotype is 112 mm long, its lateral diameter 

 increasing from 22.5 mm near the base to 41 mm near the top, the 

 apical angle being 16°. The cross section apparently is circular, but 

 only the ventral half of the specimen remains, the dorsal half 

 having weathered away. The siphuncle is centrally located. Thir- 

 teen camerae occupy a length equal to the diameter of the conch. 

 Where the diameter of the conch is 41 mm, the maximum diameter 

 of the siphuncle is estimated as 11.5 mm. The concavity of the septa 

 and the height of the camerae are estimated to average 7.5 and 3.5 

 :qfim, respectively. Where the lateral diameter of the siphuncle is 

 11.5 mm, that of the passage of the siphuncle through the septum is 

 8 mm. The inner margin of the septum extends about 3 mm inward 

 from the vertical projection of the outer margin of the septal rings. 

 These rings are in contact with the septa both above and below for a 

 radial width of 2 mm. The interior of the siphuncle is filled with 

 typical actinoceroid deposits, leaving an endosiphuncular passage 

 6 mm wide and its narrow, somewhat forward bending diverticula 

 between the outer margin of the connecting rings. The camerae of 

 the older part are almost filled with the calcareous matrix, which 

 becomes gradually less toward the younger end. 



This species is characteristic in having a rather large conch, a small 

 ratio between the diameter of the siphuncle and that of the conch, and 

 a large endosiphuncle. I am not acquainted with any American, 

 European, or Oriental species with which this is likely to be con- 

 founded. 



The specific name is given in honor of Dr. C. E. Eesser, of the 

 United States National Museum, from whom I have received valuable 

 assistance in this work. • 



Formation and locality. — ^Middle Ordovician, Ssuyen formation: 

 Lower fossil horizon of the black banded limestone beds, near Tou- 

 fang-kou, 2.5 miles northwest of Pen-hsi-hu colliery, Liao-tung, 

 Manchuria. 



Holotype.— V.S.'^M. No. 83710. 



ARMENOCERAS COULINGI (Graban) 



Plate 17, Figukb 5 



1903. Actinoceras (Ormoceras) aff. tenuifilum Ceick, Geol. Mag., new ser., vol. 



10, p. 481, pi. 22, fig. C, Dec. 4. 

 1920. Actinoceras (Ormoceras) sp. indt. Yabe, Palaeontology of southern China, 



p. 52, pi. 19, fig. 9. 

 1922. Actinoceras coulingi Geabau, Pal. Sinica, ser. B, vol. 1, fasc. 1, p. 82, 



pi. 8, fig. 1, 2. 

 1927. Actinoceras coulingi Kobayashi, Jap. Journ. Geol. and Geogr., vol. 5, no. 



4, p. 193, pi. 21, fig. 6. 



