FORMATIONS AND FOSSIL.S OF SOUTH MANCHURIA 99 



is nearly horizontal or curves gently downward. The inner margin 

 of the septum extends about 2 mm inward from the vertical projec- 

 tion of the outer margin of the septal rmgs. These rings are in 

 contact both above and below with the septa for a radial width of 

 1 mm. The ventral sides of the siphuncle and the camerae 

 are almost filled with calcareous matrix, which becomes less in the 

 apical part, while the dorsal portion is almost empty. Some deposits 

 of calcareous matrix, however, are found on the anterior surfaces of 

 the septa which are thin at the margin, but gradually thicken toward 

 the siphuncle and thin out abruptly, thus assuming a saucerlike shape 

 before reaching the connecting rings. Living chamber and surface 

 of the shell unknown. 



The specific name is given in honor of Dr. J. Suzuki, of the Hok- 

 kaido Imperial University in Japan, from whom I have received 

 much encouragement in this work. 



Gomfarisons. — This species may be compared with Armenoceras 

 murakamii (Kobayashi) but is easily distinguished by the larger 

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

 and the larger number of camerae in a length equal to the diameter 

 of the conch. 



Formation and locality — ^Middle Ordovician, Ssuyen formation: 

 Lower fossil horizon of the black banded limestone, near the Pen-hsi- 

 hu colliery, Liao-tung, Manchuria. 



Eolotype.—TJS.'EM. No. 83736. 



ARMENOCERAS TANI (Graban) 



Plate 21, Figuee 7 ; Plate 14, Figure 2 ; Plate 40, Figure 3 

 1922. Actinoceras tani Grabau, Pal. Sinica, ser. B, vol. 1, fasc. 1, p. 80, pi. 7, 



figs. 4r-l. 



This species shows a rather wide distribution in North China, 

 Manchuria, and possibly Korea. 



Descriftion. — A rather good specimen 63 mm long has a lateral 

 diameter increasing from J.7 mm near its base to 25 mm at a point 

 39.5 mm farther up, the apical angle being 12°. The cross section 

 apparently is a little depressed, but only the ventral half of the 

 specimen remains. Eight and one-half camerae occupy a length 

 equal to the diameter of the conch. The siphuncle is 8.5 mm in 

 diameter at the top of the specimen, the ratio of its diameter to the 

 lateral diameter of the conch being 1 : 3. The concavity of the septa 

 averages 3 mm. Where the lateral diameter of the siphuncle is 8.5 

 mm, that of the passage of the siphuncle through the septum is 4.5 

 mm. As is seen in the illustration, both the overlying and under- 

 lying connecting rings are adnate to the immediate septa for a 



