Vol I. 



Grabau — Ordoviciaii' Fosfiils from North China 



(1) .53 



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

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

 broadly 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. Camerse unknown, but their existence is apparently 

 indicated by the annulations of the siphuncle. 



Measuremeyits : Diameter at aperture of alveoli 35 mm. ; 

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

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

 mm. 



Horizon and Locality: A single specimen of this ^-^ ig_ chMiocra. chi.o- 



species (PL II figs. 13 a-b) was oljtained l)y Dr. F. F. Mathieu """.'/'""'■"•'■■'•. Diagrammatic sect- 

 ion along line o - p. in fig. 1-t 



from the weathered, iron-stained Peilintze limestone at Peilintze, and line s-t. in fig. 15 {nota- 

 associated with tlie preceding species and with Arducocyathus tionsas infigs. i4 and r,), 

 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 

 the early part of the siphuncle, so-called, is entirely devoid of surrounding camero?. The 

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

 this part of the shell. This lias l)een fully descrilied by Whiteaves and especially hj 

 Ruederaann, who in discussing the siphuncle of Proterocameroceras hra'nierdi from the Fort 

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

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

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

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

 and then gradually expands again".* 



* R. Ruedemann - Cephalopoda of the Leekniantown nnd Chazy formations of the Champlain Region. New 

 York State iluseum, Balletin 'JO p. 407, 1906. ^Vt' al.v> R. Ruedemann, Structnre of sunie primitive Cephalopoda. 

 Annual Report State PaUrontologist N. Y, 1903, N. Y. State Museum Bull. £0 p. 2Ud. I regret tliat I have not had 

 available, until after this paper was in type, this most searching study of tire structure of tlie primitive Cephalopcda hy 

 this eminent palaeontologist, and that my reference could, therefore, not he as extensive as was desirable. 



