FOEMATIOITS AND FOSSILS OF SOUTH MANCHURIA 81 



ARMENOCERAS ASIATICUM, new species 



Plate 16. Figxtees 2-6 



1927. Actinoceras tani Kobayashi (not Grabau), Jap. Journ. Geol. and Geogr., 

 vol. 5, no. 4, p. 192, pi. 20, fig. 9 ; pi. 21, fig. 5 ; pi. 22, figs. 1 a-b. 



This species has a rather wide distribution in Manchuria and I 

 have obtained four fragmental but comparatively well-preserved 

 specimens on which to base the following description : 



Description. — The best specimen is 43 mm long (pi. 16, fig. 3), 

 enlarging laterally from a diameter of 14 mm at the base to 21 mm 

 near the top, the apical angle being 12°. The cross section appar- 

 ently is elliptical laterally, but only the ventral half of the specimen 

 remains. Eight camerae occupy a length equal to the diameter of 

 the conch. The siphuncle is about central in its position, its diameter 

 is 5.5 mm near the top, the ratio of its diameter to the lateral diam- 

 eter of the conch being 7 : 25. The concavity of the septa is 3 mm. 

 In this specimen only the overlying connecting ring is adnate to the 

 intermediate septa for about 1 mm in width in the area immediately 

 surrounding the passage of the siphuncle through the septa, but the 

 underlying connecting rings are not adnate to the septa immediately 

 above, as they meet the inner margin of these septa at a very acute 

 angle, without a distinct septal neck intervening. The anterior 

 parts of the segments of the siphuncle are somewhat depressed as 

 compared with its posterior parts. The interior of the siphuncle is 

 filled with calcareous deposits, except the endosiphuncular passage 

 and its diverticula. The septa are thickened by the deposition of 

 calcareous matrix on the anterior surfaces, which are comparatively 

 thin at the margin, gradually thickening toward the siphuncle, and 

 then abruptly thinning out, finally assuming a saucerlike shape 

 before reaching the connecting rings. 



Comparisons. — The general characters of this species closely 

 coincide with those of Armenoceras tani {Actinoceras tani 

 Grabau), but in this species only the overlying connecting ring is 

 adnate to the intermediate septa for a short distance in the area 

 immediately surrounding the passage of the siphuncle through the 

 septa, while in the latter species both the overlying and the under- 

 lying connecting rings are adnate to the intermediate septa. More- 

 over, the former species has a smaller ratio between the diameter 

 of the siphuncle and that of the conch as compared with that of 

 the latter species. 



The specimens described by Kobayashi as Actinoceras tani are 

 exactly the same as my new species Armenoceras asiaticum in having 

 the inner margins of the septa adnate to only the upper connecting 



