(i) 50 Palueontologia Sinica Ser. B 



The older portion of the siphuncle is filled solidly with crystalline calcium 

 carbonate, this occupying the entire space between the wall of the endocone (final 

 endosheath), and probably its endo-siphuncular prolongation, and the wall or shell of the 

 siphuncle. There are however indications of one or more earlier endosheaths (See sections 

 figs. 11 and 12 Plate II, and Plate V middle figure): The difference in the character of 

 the outer zone of the solid portion of the siphuncle from that forming the inner portion, 

 observable both in the worn specimen (Plate V, middle figure) and in the sections (Plate 

 II figs. 11 and 12) suggest that at first the siphuncle was filled with closely set 

 endosheaths (which in the large specimen of the group on Plate V formed a thickness of 

 about 7 mm.), and then crystalline calcium carbonate (aragonite?) was deposited by the 

 animal, without further formation of definite endosheaths, until the final one was formed 

 by the adult animal. The appearance of these older endosheaths suggests their similarity 

 to those of Piloceras, or to a primitive form from which both Chihlioceras and Piloceras 

 were derived.* 



The wall or shell of the siphuncle is thin but continuous. It is annulated, though 

 indistinctly so, near the apical portion, while forward, the annulations become pronounced 

 and regular. The annuli present a long gently convex forward slope and a shorter more 

 abrupt, but still convex apical slope. There are 10 of these annuli in the space of 35 mm., 

 giving them an average width of 3.5 mm. There is however a gradual increase in the 

 width, the posterior ones being less than 3 mm. wide. The depressions between the 

 annuli are very shallow. While this is the character in the earlier portion of the 

 siphuncle, continuing for varying lengths in different specimens, it gradually changes in 

 the later -formed portion, where the annuli become narrowly rounded, with broad gently 

 concave interspaces. In the specimen shown in fig. 13 PL IV, this type of annulation 

 begins about 30 mm. from the apex, and there are 10. annuli in the space of 38 mm., 

 these also increasing slightly in width forward. 



The annuli are oblique, bending forward on the ventral side. The angle which 

 they form with the axis of the siphuncle on the side of the siphuncle, was found in one 

 case to be about 30 degrees, but less than that in another specimen. . Their ventral aspect 

 is unknown. 



Camera? not known, none of the specimens showing any indications of them 

 other than the annulations of the siphuncle. Though this annulation is suggestive of a 

 camerate nature of the shell, it is not a positive indication, as camerate shells with 



* In the locality from which these specimens were obtained, they are restricted to the lower division, while 

 Piloceras occurs in the higher division, with one doubtful representation in the lower. 



