linNjEan arrangement. 23 



Cyprau. Shell with the aperture efHise linear ; teeth on both 



sides. 

 Bulla. Shell with the aperture somewhat contracted, ol)li([ue. 

 Voluta. Shell with the aperture efflise, with the pillar folded. 

 Buccinum. Shell with the aperture with a channel to the right. 

 Strombus. Shell with the aperture having a channel to the left. 

 Murex. Shell with the aperture having* a straight channel. 

 Trochus. Shell with the aperture compressed, somewhat square. 

 Ttirbo. Shell with the apertvu'e compressed, round. 

 Helix. Shell with the aperture compressed, moon-shaped. 

 Nerita. Shell with the aperture compressed, half round. 

 Haliotis. Shell with the aperture wide, bored. 



UNIVALVES without a regular spire. 



Patella. Shell an open cone, resting. 



Dentalium. Shell free, awl-shaped, open at each end. 



Serpula. Shell fixed, tubular. 



Teredo. Shell intruded in wood. 



