514 



MOLLUSCA 



SUB-KIXGDOM VI 



or cicatrix, which is more or less compressed elliptical, never transversely elliptical or 

 depressed, and is sometimes hidden by the protoconch or its shrunken remnants. 



The order may be subdivided according to the general external features of 

 the shell and structure of the siphuncle into five sub-orders, as follows, named with 

 reference to peculiarities of the funnels : Holochoanites, Mixochoanites, Schistochoanites, 

 Orthochoanites, Cyrtochoanites. The characters of these different groups are denned 

 under their proper headings. 



Sub-Order A. HOLOCHOANITES. Hyatt. 



Funnels of siphuncular segments reaching from the septum of origination to the plane 

 of the next septum apicad or beyond this, or in some genera even to the plane of the second 



I. DlPHRAGMIDA. 



This group contains but one family, Diphragmidae, having the same characters as 

 the following unique genus : 



Diphragmoceras, Hyatt. Orthoceracones and cyrtoceracones having simple septa 

 and sutures as in Endoceratida, but siphuncle divided by tabulae alternating with the 

 septa of the camerated shell. Chambers of siphuncle empty, as are also the camerae. 

 Quebec Group. 



II. ENDOCERATIDA. 



Orthoceracones, cyrtoceracones, gyroceracones, and nautilicones having siphuncles of 

 variable diameter, but as a rule large in proportion to width of the shell. TJiey may be 



empty or filled with internal 



B c organic deposits, but are in- 



variably tubular, and the 

 funnels completely shut off the 

 interior from the interiors of 

 the camerae. The latter are 

 without organic deposits. 



Family 1. Endoceratidae. 



Smooth or annulated ortho- 

 ceracones. Siphuncle always 

 more or less filled ivith organic 

 deposits. 



Vaginoceras, Hyatt (Fig. 

 1055). Ordovician. Gamer o- 

 ceras, Conrad (Sannionites, 

 Hyatt ; Suecoceras, Holm). 

 Ordovician and Silurian. 



Endoceras, Hall (Colpo- 

 ceras. Hall; Diploceras, Con- 

 rad), (Fig. 1056). Smooth 

 or annulated Orthoceracones. 

 Funnels reach from septum 

 of origination to the next 

 apicad of this, but .no farther. 

 Organic deposits in the form of endocoiies, 



Fio. 1055. 



A, Vaginocci-i'* (End.) duplex, Walilb. Ordovician ; Kinnekulle, 

 Sweden. Much reduced. B, V. commune, Wahlb. Ordovician - Oranien- 

 baum, Russia. The anterior endocone of the siphuncle is filled up 

 with matrix so as to form a dart (" Spiess "). V 2 . C, Diagrammatic 

 longitudinal section of the last, showing siphonal funnels. D, De- 

 tached camera of Vaginoceras with long siphonal funnel. (Figs. C 

 and D after Dewitz.) 



Septa pass entirely around the siphuncle. 



