FORMATIONS Al^D FOSSILS OF SOUTH MAE^CHUEIA 103 



side of the conch has been weathered away, so as to expose the septa 

 and the siphuncle. The siphuncle is somewhat ventral of the center 

 of the conch. It is estimated that 7 camerae occupy a length equal 

 to the diameter of the conch. Where the diameter of the conch is 

 19 mm, the concavity of the septa is 2.7 mm ; the maximum diameter 

 of the siphuncle here is estimated at 5.5 mm, and the height of its 

 camerae averages 2.7 mm. The segments of the siphuncle are rather 

 globular, but slightly depressed vertically at its anterior contacts 

 with successive segments. The septal necks are short, usually 0.5 

 mm or less in length. The interiors of the siphuncle and the cam- 

 erae of the lower part of the specimen are occupied by dense cal- 

 careous matrix, which becomes less toward the apical end. Living 

 chamber and surface of the shell unknown. 



The specific name is given in honor of R. Kimura, director 

 of the geological institute. South Manchuria Railway Co. 



Formation and locality. — Middle Ordovician, Ssuyen formation: 

 Lower fossil horizon of the black banded limestone beds just east 

 of the Mu-hsin-tai colliery, Liao-tung, Manchuria. 



Eolotype.—V.^.'^M. No. 83746. 



ORMOCERAS MANCHURIENSE. new species 



Plate 27, Figure 6 ; Plate 40, Figuee 16 



Description. — The holotype, 80 mm long, enlarges slightly later- 

 ally from the base to the top. The dorsoventral diameter of conch 

 near the top of the specimen is estimated as about 44 mm, while the 

 lateral diameter at the same place is about 32 mm. The cross section 

 of the conch is apparently compressed, while that of the siphuncle 

 is circular, but only the lateral half of the specimen remains. The 

 siphuncle evidently was located rather ventral of the center of the 

 conch. It is estimated that 3 camerae occupy a length equal to the 

 dorsoventral diameter of the conch. AYhere this dorsoventral 

 diameter is 43 mm, the concavity of the septa is 29.5 mm ; the maxi- 

 mum diameter of the siphuncle here is estimated at 23 mm, and the 

 height of its camerae varies from 13.5 to 15 mm. The siphuncle is 

 rather nummuloidal. The septal necks are short, usually 1.5 mm or 

 less in length, with their lower margins flaring widely where they 

 unite with the connecting rings. Both sides of the septa and the 

 interior of the siphuncle are filled with calcareous deposits, but the 

 usual central endosiphuncular passage and its lateral deverticula 

 into the outer margin of the annulation lack such deposits. 



Gom'parison. — This form differs from other species of Ormoceras 

 in having a larger siphuncle, a great concavity of the septa, and 

 comparatively higher camerae. 



