FORMATIONS AND FOSSILS OF SOUTH MANCHTJEIA 95 



apical angle being 14°. The cross section apparently is elliptical 

 laterally, but only the ventral half of the specimen remains, the 

 dorsal half having weathered away. Eight camerae occupy a length 

 equal to the diameter of the conch. The siphuncle is excentric, the 

 distance between the siphuncle and ventral side of the conch being 

 4.5 mm at the top. Where the diameter of the specimen is 24.5 mm, 

 and the septa 3.5 mm apart, segments of the siphuncle have a maxi- 

 mum diameter of 10.1 mm at mid height, constricting to 4.5 mm 

 at its passage through the septum, with the result that the siphuncular 

 segments form depressed nummuli. The concavity of the septa 

 averages 4.7 mm. Between; the connecting rings the septa are 

 horizontal, and there is no trace of a septal neck. The interior of 

 the siphuncle is filled with typical actinoceroid deposit, leaving the 

 comparatively large endosiphuncular passage with its narrow, lateral 

 diverticula into the outer margin of the connecting rings. Septa 

 are somewhat thickened by the deposition of the calcareous matrix 

 which occurs on both the upper and under sides of the septum. 



Go7nparisons. — This species may be compared with Armenoceras 

 richthofeni (Freeh), but the smaller apical angle, the shallower 

 septal concavity, the comparatively narrower siphuncle, and the 

 shorter septal neck serve readily to distinguish it. 



Formation and locality. — Lower Ordovician, Wuting formation: 

 In the black banded limestone beds, near the second tunnel, 1 mile 

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



Eolotype.—{].^.'^M. No. 83706. 



ARMENOCERAS PENHSIENSE. new species 



Plate 20, Figube 6; Plate 40, Figure 15 



Description. — The holotype, 67 mm long, enlarges very slightly 

 in a length of 39 mm at the upper part of the specimen. This speci- 

 men shows a dorsoventral longitudinal natural section. The cross 

 section of the conch and siphuncle, however, apparently are circular. 

 The siphuncle is very excentric, its center being located 8.5 mm from 

 the ventral wall of the conch. Where the dorsoventral diameter of 

 the conch is 29 mm, the concavity of the septa is 7.5 mm ■ the maxi- 

 mum diameter of the siphuncle here is estimated at 12 mm, and the 

 average height of its camerae is 5.5 mm. There are about 5.1 camerae 

 in a length equal to the dorsoventral diameter of 29 mm. Between 

 the connecting rings the septa are horizontal, and there is no trace 

 of a septal neck ; the inner margin of the septa extends about 3.7 mm 

 inward from the vertical projection of the outer margin of the septal 

 rings. The interior of the siphuncle is filled with calcareous matrix, 

 leaving an endosiphuncular passage 1.5 mm wide, with its lateral 

 diverticula, into the outer margin of the connecting rings. The 



