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PALAEONTOLOGY. 



Order 1. — Teteabranchiata. 



(Nautiloid Cephalopoda?) 



Branchiae in two pairs, without branchial hearts ; funnel 

 formed by a convolute muscular plate ; mantle thin, and 

 feebly muscular ; no ink-bag ; arms very numerous, hollow, 

 and with retractile tentacula ; mandibles with calcareous tips ; 

 eyes pedunculate ; head retractile, within a shell, which is 

 external, many chambered, siphunculate, the outer layers 

 porcellaneous, the inner layers and partitions nacreous. 



Fig. 29. 

 Nautilus Pompilius. 



Genus Nautilus, Linn. — Shell discoid, symmetrical, with 

 the apertures, sutures, and siphuncle, simple. The anatomical 

 characters of the order are also those of the sole existing genus. 

 It is the representative of numerous genera and species of 

 chambered Cephalopods that abounded in the Palseozic and 

 Secondary periods, but which seem to have been superseded, 



