146 



having two valves incrusted on one side of the club. The disk at the end of the 

 club convex and perforated with subtubular holes, having a fissure in the centre. 

 A. Javanum, A. vaginiferum, A. Novse Zeylandise, A. agglutinans. 



Clavagella. Sheath tubular, testaceous; the anterior end attenuated and 

 open; the posterior club-shaped, ovate and rather compressed, with spinous 

 tubes; one valve fixed in the side of the club, the other free in the tube. 



C. apcrta. 



Fistulana. Sheath tubular, mostly testaceous; the posterior closed and 

 turgid; the other end attenuated and open at the summit, inclosing a free bi- 

 valve shell, the valves of which are equal, and gape when closed. 



F. clava, F. corniformis, F. gregata, F. lagenula. 



Septaria. Tube testaceous and very long, gradually diminishing towards 

 the anterior end; the interior divided by arched partitions, usually incomplete; 

 the anterior extremity terminated by two other slender tubes, which are not 

 divided internally. 



S. arenaria. 



Teredina. Sheath testaceous, tubular, cylindrical; the posterior ex- 

 tremity closed, showing the two valves of the shell; the anterior end open. 



Teredo. Tube testaceous, cylindrical, flexuous, open at both ends, not 

 belonging to the shell, and covering the animal. Shell bivalve, situated pos- 

 teriorly on the outside of the tube. 



T. navalis, T. palmulatus. 



PHOLAD ARIA.— Two Genera. 



Shell without a tubular sheath, having accessary pieces which do not belong 

 to the valves, and gapes anteriorly. Ligament external. 



Pholas. Shell bivalve, equivalve, transverse, gaping at both sides, 

 having various accessary, testaceous pieces affixed above or below the hinge. 

 The inferior or posterior margin of the valves reflected outwards. 



P. dactylus, 

 ' orientalis, 

 ' candidus, 

 ' dactyloides, 



