Vol I. 



Qrabau, Ordovician Fossils Jrom North China 



(0 53 



This indicates that on the ventral surface they formed a broad, low, forward arching 

 curve or saddle, though the actual condition has not been observed. The annulations are 

 l>roudly and regularly rounded and separated by concavities of equal form and width. 

 There are six annulations in the space of 18 mm. giving an 

 average width, between the centers of adjoining concavities, of 

 3 mm. Camera? unknown, but their existence is apparently 

 indicated by the annulations of the siphuncle. 



Measurements : Diameter at aperture of alveoli 35 mm. ; 

 at point of confluence of lateral alveoli 28 mm. Width of 

 median alveolus at base 13.5 mm.; height of same 10 

 mm. 



HORIZON AND LOCALITY: A single specimen of this Fij? 1G ChMiwm , ,.,,,_ 



Species (PI. II figs. 13 a-b) Was Obtained by Dr. F. F. Mathieu wangtaoeme. Diagrammatic sect- 

 ion along line o-j>. in fig. H 



from the weathered, iron-stained Peilintze limestone at Peilintze, ant i ij ne s .t. ; &%. 15 

 associated with the preceding species and with Archseocyathus tlonsas mfi 8 - H aud 1 "')- 

 etc. The horizon is Lower Ordovician. 



PHYLOGENETIC SIGNIFICANCE OF THE SIPHUNCLE 

 OF THE HOLOCHOANITES. 



It has long been known that in certain members of the suborder Holochoanites 

 tin' early part of the siphuncle, so-called, is entirely devoid of surrounding camene. The 

 genus Proterocameroceras shows perhaps the most extensive pre-camerate development of 

 this part of the shell. This has been fully described by Whiteaves and especially by 

 Ruedemann, who in discussing the siphuncle of Pmterocameroceras brainerdi from the Fort 

 Cassin or upper Beekmantown (Lower Ordovician) of Lake Champlain (U. S. A.) speaks 

 of the apical portion as " projecting beyond the chambered shell for a distant of about 75 

 mm., gradually expanding from the blunt apical end, which here has a diameter of about 

 3 mm., to 11.5 mm. at the beginning of the phragmocone, where it contracts to 10 mm. 

 and then gradually expands again".* 



* K. Ruedemann - Cephalopoda of the Beekmantown and ("hazy formations of the Champlain Region. New- 

 York State Museum, Bulletin 90 p. 407, 1906. Sue also R. Ruedemann, Structure of some primitive Cephalopoda. 

 Annual Report State PaUeontologist N. Y. 1903, N. Y. State Museum Bull. 60 p. 296. I regret that I have not had 

 available, until after this paper was in type, this most searching study of the structure of the primitive fephalopc da l>y 

 this eminent palfeontologist, and that my reference could, therefore, not be as extensive as was desirable. 



