CO^CEYLIA—DITHYRA. 3. 17 



collected from the fragment were all of the same size, and all dis- 

 tinguished by the strong conical tooth on the margin above the 

 hinge, pointing in a rather oblique direction. 



3. G ASTROOH^NA- SPENGLER. 



Testa transversa, ovata, cequivalvis, inasquilateralis, hiatu maximo. 



Cardo dente unico transversa sublaminato obsoleto, in utrdque valvd : 



lateralibus nullis. Ligamentum externum. 

 Shell transverse, oval, ecjuivalve, inequilateral, with a vast opening. 



Hinge with a single transverse somewhat laminar obscure tooth 



in each valve : lateral teeth none. Ligament external. 



In its habits this genus approaches very near to that of the 

 Pholas, living in the interior of rocks and stones covered by the sea, 

 where it forms an outer testaceous coat, in which the shell itself is 

 imbedded, surrounded by a slimy mucus : and this outer case, 

 which is formed upon the inner surface of the decomposed rock, 

 is quite smooth, extending beyond the rock itself, and is partly 

 divided at the end, like the tube of the Teredo navalis, for the 

 protrusion of the two terminal lobes of the animal. In the mid- 

 dle of the wide opening of the shell, the animal is furnished 



D 



