(i) G6 PaJseontologia Sinica Ser. B 



This genus is closely related to Loxoceras, McCoy, with which it agrees in the 

 character of the siphuncle. Its distinctive character however is seen in the development 

 of the compound septa, or septa and pseudosepta, with stereoplasmic deposit between. 

 In ' these respects the genus is related to Actinoceras. Indeed this genus may be 

 considered as intermediate between Loxoceras, and Actinoceras, partaking of some 

 characters peculiar to the one and of others characteristic of the other. 



The exterior of the shell is unknown except that it is not annulated. So far as 

 can be ascertained, the surface is smooth. Expansion is regular, and although the living 

 chamber is still unknown, there is no reason for assuming that it is other than in 

 Orthoceras. 



Genotype. Stcreoplasmoceras pseudoseptatum Grabau, Ordovician. 



It is highly probably that the specimen figured by Crick as Orthoceras or Actino- 

 ceras (Geol. Mag. New Ser. Dec. IV. Vol. X, PI. XXII fig. A) belongs to this genus, for 

 as far as can be ascertained from the reproduction of the photograph it shows the pseudo- 

 septa and stereoplasmic filling of S. pseudoseptatum. 



Stereoplasmoceras pseudoseptatum Grabau (sp. nov.) 



Plate VI, figs. 5-7. Plate IX, fig. 11. 



Shell regularly tapering, apparently at a variable rate, though this may be due to 

 the variation in direction in which the sections are cut. In a specimen from Lincheng, 

 Shantung (cat. no. 80) the rate of tapering appears to be 1 in 6.5 while in a sectioned 

 specimen from Ningyang Shantung (Plate VI, fig. G cat. no. 57) it is only 1 in 12.5. 

 Still another section of an typical specimen from Tangshan (Plate VI, fig. 5, cat no. 58) 

 shows a rate of tapering of 1 : 9. 75. These variations are probably due to the fact that 

 the sections are cut somewhat obliquely and so do not give the true rate of tapering. The 

 true rate lies probably between the two extremes - i.e. about 1 : 9. 



Section subcircular, apparently a little flattened on one side. Septal distance 

 about 4.6 mm. (varying in the different specimens from 4.5 (rarely 4) to 4.7, the shell 

 diameter varying from 25-30 mm. but not in the same proportion). Towards the 

 apertural end in the longer specimens, the interval increases to 5 mm. or to a little more, 

 the maximum shell diameter observed being somewhat less than 40 mm. The depth of 

 the septa is from 1 \ to 1 f camera. The septa are conspicuously compound, owing to 

 the numerous pseudosepta. On the upper side of the septum, the pseudosepta extend about 



