DIBEAXCHIATE CEPHALOPODS. 



91 



quite prolDable that this genus really belongs to the Beleni- 

 nitidce. 



Kg. 4':6.—Spindirostra Bellardii. Miocene Tertiary. 



cl. Belemnosis. — This genus has been founded for the re- 

 ception of an Eocene fossil closely resembling Bcloptera, but 

 differing in not possessing any lateral expansions. This 

 genus also probably belongs to the family Belemnitidce. 



YxM. 5. Spieulid^e. — Shell (fig. 447, c) nacreous, dis- 

 coidal, composed of volutions which are not in contact with 

 one another. The shell is di\dded into a series of air- 

 chambers by curved shelly partitions, pierced by a ventral 

 tube or " siphuncle." The entire shell corresponds with the 

 " phragmacone " of the skeleton of the Belemnites. Spiruli- 

 rostra and Beloptera are often referred to this family ; but if 

 these be placed in the Sepiadce, the family of the Spindidce 

 is then without any known fossil representative. 



Fam. 6. Belemxitidje. — Shell internal, composed of a coni- 

 cal chambered portion (" phragmacone "), with a marginal or 

 ventral siphuncle, lodged in a cylindrical fibrous "guard," 

 and produced in front into a thin horny or shelly plate or 

 " pen " (the " pro-ostracum "). The Belemnitidce are almost 

 exclusively confined to the Secondary rocks, ranging from 

 the top of the Trias to the Chalk, inclusive. Quite recently 

 Professor Tate has described a species of Belemnite from 

 strata of supposed Tertiary age in Australia ; and another 

 form has been recorded from Eocene deposits in Europe. 



