94 BULKETIN 16 4, UNITED STATES NATIONAL MUSEUM 



2.5 miles northwest of Pen-hsi-hu, and from the same horizon, near 

 Wu-hu-tsui, Liao-tung, Manchuria. 



Holotype and paratype.—U.S.'NM. Nos. 83728 and 83729. 



ARMENOCERAS NUDUM, new species 



Pi^TE 20, Figure 1 ; Pi^tb 40, Figure, 13 



Description. — The holotj'pe, 84 mm long, enlarges from 13 mm 

 near the base to 25 mm at a point 56 mm farther up, the apical angle 

 being about 15°. The cross section on the conch apparently is later- 

 ally depressed, while that of the siphuncle is circular, but only the 

 ventral part of the specimen remains, the dorsal half having been 

 weathered away. The siphuncle is excentric, its center located 5.5 

 mm from the ventral wall of the conch. Where the diameter of the 

 conch is 24.5 mm, the concavity of the septa equals 4.5 mm; the 

 maximum, of the siphuncle here is estimated as 7 mm, and height of 

 its camerae averages 3.5 mm. Therefore, the ratio of the diameter of 

 the siphuncle to that of the conch is 29 : 100. There are seven camerae 

 in a length equal to the diameter of the conch. The inner margin 

 of the septa, at the passage of the siphuncle through it, curves down- 

 ward very slightly. Both the overlying and the underlying connect- 

 ing rings are adnate to the intermediate septa for 1 mm in width, on 

 the average, in the area immediately surrounding the passage of the 

 siphuncle through the septa. The interior of the siphuncle is filled 

 with typical actinoceroid calcareous matrix, but the narrow endo- 

 siphuncular passage and its diverticula into the outer margin of the 

 connecting rings lack such deposits. The septa are slightly thickened 

 with the deposition of the calcareous matrix chiefly on the anterior 

 but in some cases, also slightly on the posterior sides of the septa. 

 Most of the camerae, however, are empty. This emptiness of the 

 camerae is the most marked feature of the species, and, together 

 with the comparatively narrower siphuncle and other details, serves 

 to differentiate it from the others. 



Formation and locality. — Middle Ordovician, Ssuyen formation: 

 A black limestone bowlder believed to have come from the Ssuyen 

 formation, in river drift at the Niu-hsin-tai colliery, Liao-tung, 

 Manchuria. 



Holotijpe.—V.S.Hii.M. No. 83730. 



ARMENOCERAS NUMATAI, new species 



Plate 26, Figure 11 ; Plate 40, Figure 7 



One rather good specimen of this new species was given me by 

 H. Numata, a teacher at the Antung Middle School. 



Description. — The holotype is 55 mm long, enlarging from a 

 lateral diameter of 17.5 mm at the base to 26 mm at the top, the 



