PLATE VII. 



Upper Ordovician Cephalopods: — MarJiiaJcou Limestone. 



Drawings by K. C, Liu (fiJ^K;^) 



Fig. 1. Actinoceras riclithofeni Freeh p. 75 



An average adult individual weathered so as to show siphuncle. The specimen 

 probably represents a little more than half the original length. Natural size. 

 Machiakou limestone, Tangshan, Chihli. (T. C. Wang Coll. G. S. Ch. Cat. 



No. 5). 



Fig. 2. Actijioceras richthofeni Freeh p. 75 



Portion of a polished rock surface showing the apertural end of the siphuncle in 

 section. The gradual thickening of the septal rosettes is shown. Also a portion of 

 the camerate part of the shell is shown. Natural size. Machiakou limestone, 

 Huo-Luh, Chihli. (Coll. lAliss Clarke; G. S. Ch. Cat. No. 13). 



Fig. o. Actinoceras richthnfvni Freeh p. 75 



A portion of a weathered section of the siphuncle, showing the rosettes around the 

 septal necks and the nature of the endosiphuiiele and its diverticula. Enlarged 

 three times. ALnchiakou limestone. Tangshan, Chihli. (T. C. Wang coll., C. S. 

 Ch. Cat. No. 5). (See also plate IX). 



Fig. 4. Actinoceras tani Grabau p. 80 



4a. Longitudinal section showing open endosiphuncle. Natural size. 

 4b. Transverse section. Natural size. Machiakou limestone, Kushan, Huo-Luh-Hsien, 

 Chihli. (Cotype, G. S. Ch. Cat. No. 69). 



Fig. 5. Actinoceras tani (Jrabau p. SO 



The lower end of a typical specimen showing blunt apical portion, rate of tapering 

 and, in upper part, septa and siphuncle. Natural size. Machiakou limestone, 

 Tangslian, Chihli. (Cotvpe, Coll. Messrs. Morris, Terrill & Barbour, G. S. Ch. Cat. 

 No. 26). 



Fig. 6. Actinoceras tani Grabau p. 80 



Natural weathered section, showing siphuncle with part of endosiphuncle exposed, 

 and the nature and amount of the stereoplasm in the camera?. Machiakou lime- 

 stone, ^fa-Chia-Kou, Chihli. (Cotype, H. C. T'an coll. G. S. Ch. Cat. No. 1). 



Fig. 7 Actinoceras tani Grabau p. SO 



7a. Apical portion of a characteristic shell, showing form, slight constriction and 



sutures. Also the large subconical initial eliamber. Natural size. 

 7b. Apical view of the same showing the scar of the siphuncle with its swollen rim, 



situated subcentrally at this end; at the upper end of the fragment the siphnncle is 



strongly excentrie. Natural size. 

 7e. A single nummulus of the siphuncle, with surrounding septal portion enlarged X 



4, to show the mural pores on the periphery. Machiakou limestone, Tangshan. 



(Cotype, Coll. ^Messrs. Morris, Terrill and Barbour, G. P. Ch. Cat. No. 16). (See 



further, plate IX) . 



Fig. 8. Actinoceras nanum (Irabau p. S7 



Natural section of the apical portion of a typical specimen, showing the small 

 siphuncle with its endosiphuncle, the- septa, and rate of tapering. Natural size. 

 Machiakou limestone, Tangshan, Chihli. (Holotvpe, T. C. AVang Coll. G S Cli 

 Cat. No. 8) . (See also plate IX) . 



120 



