MOLLUSCA — CEPHALOPODS 



251 



Scaphopods are marine and live embedded 

 in mud and sand, usually at great depths. 

 They range from the Ordovician to the 

 present. Dentalium, the tooth shell, ranges 

 from the Tertiary to the present (Fig. iii). 



CLASS E, CEPHALOPODA 



Type of the class, Xautilus pompilius 

 (Fig. 112). 



The pearly Nautilus lives in moderately 

 shallow or deep water in the South Pacific, 

 usually creeping about on the bottom. The 

 body is inclosed in a coiled shell, secreted 

 by the mantle, from which project the head 

 and tentacles when the animal is moving 

 and into which they may be withdrawn for 

 protection. The appearance of Nautilus, 

 with its expanded tentacles surrounding the 

 head, is similar to that of the disk of a sea- 

 anemone. The shell consists of an elongate 

 cone coiled in one plane and is divided by 

 transverse partitions (the septa) into a series of chambers. 

 The soft body of the animal is lodged in the wide end of the 

 cone in front of the last formed septum ; this cup-like chamber 

 in which it lies is called the living chamber. An extension 

 of the body, the siphon, passes backward from the Uving cham- 

 ber, through perforations in the septa ; it thus maintains con- 

 nection with the earliest formed chambers in the apex of the 

 shell. 



This siphon is really just an extension of the coelome or body 

 cavity of the animal, a tubular extension opening from the pos- 

 terior portion of the coelome. An artery extends through its 

 entire length, finally ending openly. Though the siphon narrows 

 where it passes through each septum yet its cavities are not 

 effaced. 



■post 



Fig. III. — A scapho- 

 pod, Dentalium at- 

 tentiatum Say, which 

 lived in the seas 

 covering eastern 

 Maryland during 

 the Miocene, ant., 

 anterior aperture ; 

 dor., dorsal side of 

 shell ; post., posterior 

 aperture. Length of 

 shell 2.T, inches. 

 (After Martin.) 



