146 



Figure. 



Lutraria arcuata. PI. 40. Kg. 219. Shell, with one valve dropped 

 to show the Mactra-like teeth and ligameiit-pit. 



Family 10. MYARIA. 



Shell; mostly gaping at each end; ligament sometimes internal, 

 supp>orted bg a spoon-shaped process, in connection in many in- 

 stances with a detached ossicle, sometimes external, supported 

 on a thickened ledge or fulcrum. 



The genera of this family are extremely varied in character, and yet they 

 are linked together by a marked sequence of affinity. Chamostrea is a 

 convex C/iama-\\ke adherent genus, but the ligament, which is internal, 

 has in connection with it a detached shelly appendage or ossicle, which 

 appears in Anatina, the type of a quite distinct section. In Anatina the 

 animal's siphons are enclosed in a wrinkled epidermic sheath, which is de- 

 veloped to a very large extent in Mya, Panopaa, Glycimeris, and Phola- 

 domya, yet so inconstant is the structure of the shell's hinge, that whilst 

 in one genus it is internal, lodged in a projecting cavity, in another it is 

 external, supported on a ledge or fulcrum. The genera are thirteen, as 

 follows : — 



Genus 1. CHAMOSTREA, Eoissy. 



Animal ; mantle-lobes united by their extreme edge between the 



pedal orifice and siphons ; pedal opening small, toith a minute 



ventral orifice behind it ; siphons a little apart, very short, 



denticulated ; body oval, terminating in a small compressed 



foot. fHancock.J 



Shell ; inequivalve, CI Lama-shaped, with the umboes involute, some- 

 what pearly in the interior, attached to rocks by the anterior side 

 of the right valve, which is very convex ; left valve flat, with a 

 small conical tooth fitting into a corresponding pit to form the 





