CYRTODARIA. 351 



Genus PANOPJ2A, Menard de la Groye. 



Siphons large, separated at their ends, covered with a 

 thick, wrinkled epidermis. 



Shell equivalve, thick, transversely oblong, gaping at both 

 ends, surface nearly smooth, or transversely furrowed. Hinge 

 formed of a single conical tooth in each valve, lodged in a 

 cavity of the opposite valve ; ligament short, external, pro- 

 minent, attached to strong ridges. Pallial line interrupted, 

 with a deep posterior sinus. 



Ex. P. Norvegica, Spengler, pi. 94, fig. 3. Shell, P. 

 Norvegica, fig. 3, a, 3, b. 



The animal and shell of this genus very much resemble 

 Saxicava on a large scale, and, like that genus, the species 

 are found principally inhabiting the shores of Northern 

 countries, ranging from Ochotsk to the White Sea, Norway, 

 and North Britain. 



Species of Panopcea. 

 Middendorfii, A. Adams. Norvegica, Spengl. 



Genus CYRTODARIA, Daudin. 



Palpi large, sickle- shaped, striated inside, the hinder 

 border broad, plain; siphons large, united, covered with a 

 thick epidermis, orifices small, fringed. 



Shell equivalve, thick, oblong, transverse, gaping widely 

 at both ends, valves covered with a thick, black, horny epi- 

 dermis which extends beyond their edges. Hinge callous, 

 edentulous; ligament large, prominent, external. Muscular 



