PaRMATIO]SrS AND FOSSILS OP SOUTH MANCHUBIA 97 



extends about 2.5 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 1.5 mm. The 

 interior of the siphuncle is filled with typical actinoceroid deposits 

 of calcareous material, leaving the large endosiphuncular passage 

 and its narrow diverticula, which show a more or less forward bend- 

 ing. The septa are thickened by the calcareous matrix, which occurs 

 both on the upper and under sides of the septum, so that this matrix 

 fills in the larger part of the camerae in the older part of the speci- 

 men. Some camerae, however, especially in the apical part, were 

 empty. Surface of the conch fairly well annulated. 



Formation and locality. — Middle Ordovician, Ssuyen formation: 

 In the lower fossil horizon of the black banded limestone near Tou- 

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



Plesiotype.—V.S.'^M. No. 83732. 



ARMENOCERAS SHIMIZUI. new species 



Plate 20, Figuee 5 



Description. — The holotype is 43 mm long, enlarging very slightly 

 from the base to the top. The cross section apparently is depressed 

 but only the ventral half of the specimen remains. Siphuncle excen- 

 tric in its position, the distance of the siphuncle from the ventral 

 wall of the conch being 2 mm at the base. It is estimated that 7.2 

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

 Where the lateral diameter of the conch is 17.5 mm, the concavity 

 of the septa is 2.5 mm, the length of the camerae is 2.7 mm, and the 

 maximum diameter of the segments of the siphuncle 6 mm. There 

 are no traces of the septal necks at the inner margins of the septa, 

 which are adnate with both the upper and lower connecting rings 

 for 0.7 mm in radial width. The interior of the siphuncle is densely 

 filled with calcareous matrix. The septa are thickened regularly by 

 the calcareous matrix, which occurs both on the upper and lower 

 sides of the septum, leaving rather narrow spaces in the mid height 

 of each camera. 



The specific name is given in honor of Dr. S. Shimizu, of the 

 Tohoku Imperial University in Japan. 



Comparisons. — The general features of this species recall Armeno- 

 ceras tani, but the cylindrical conch and the calcareous deposits on 

 both sides of the septa serve readily in distinguishing it from the 

 latter species. 



Formation and locality. — Middle Ordovician, Ssuyen formation: 

 The lower fossil horizon of the black banded limestone bed, at a 

 point 2 miles east of the Tao-yuan-kou colliery, Liao-tung, Man- 

 churia. 



Holotype.— {J.S.'^.'M.. No. 83733. 



