254 



PALEONTOLOGY. 



chamber is incapable of receiving the body of the animal, as 

 is the case in the polythalamous shells of the teiitaculifera. 



FIG. 173. Ancyloceras gigas. (Lower greensand).* 



The ten-armed cephalopoda, called decapoda, with internal 

 shells, form several families. 



The SPIBULIDJS have an internal calcareous shell, formed 

 of a series of air-chambers, traversed by a siphon. It con- 

 tains living and fossil genera, as beloptera, spirulirostra, from 

 the tertiary stages of France. 



The LOLIGID^; are provided with an internal horny plate 

 of a feather-like form, without air-chambers ; several fossil 

 genera are found in the oolitic rocks. 



The TEUTHID^ have an internal plate or blade, much 

 elongated, like an arrow, without air-chambers. It contains 

 three fossil genera which belong to the Oxfordian stage of 

 the oolitic period. 



The BELEMNITLD^E have an internal horny skeleton and 

 a testaceous shell, formed of air-chambers piled on each 

 other in a straight line, and traversed by a lateral and 

 marginal siphon. All the genera of this family are extinct. 

 They are distributed throughout the rocks of the oolitic and 



* We have a noble specimen of this fossil in our cabinet, from the Isle of 

 Wight, which measures eighteen inches in length and twelve inches in depth. 



