157 



67. trigonalis, C.B.Ad. 69. tunicata, Hinds. 71. variegata, Ad. Sf Rv. 



68. truncata, Hinds. 70. ustulata, Reeve. 72. ventricosa, id. 



Figure. 



Coubula sulcata. PL 45. Fig. 239. Shell, showing the overlapping 

 growth of the right valve over the left valve. 



Genus 10. MYA, Linnmis. 



Animal ; mantle closed in front except for the passage of a mode- 

 rate conical foot ; siphons very long, united nearly to their 

 extremities, which have fimbriated orifices, and enclosed in a 

 wrinkled epidermic sheath. 



Shell ; oblong-ovate, equivalve, gaping at each extremity ; hinge 

 composed of a broad, ascending, spathulate tooth in the left valve, 

 connected by a short thick internal ligament with a correspond- 

 ing socket in the right valve. 



The genus Mya embraces two very distinct types, one represented by 

 the well-known 31. arenaria and truncata, which have a wide range of 

 habitation, especially throughout the north temperate and arctic seas, the 

 other by a few semitransparent Auatina-like forms (genus Tugonia, Gray) 

 peculiar to the shores of west Africa. In the former, which have shells 

 of rather large size and of comparatively solid structure, the hinge has a 

 broad ascending tooth in the left valve only, in the Tugonia group the as- 

 cending tooth occurs in a modified form in both valves, the shell is of 

 more delicate transparent substance, and it is more globose, with the pos- 

 terior end very widely orbicularly gaping. Of Tugonia the animal is 

 not known. Of the arctic and best-known group the animal lives buried 

 deep in the mud, with its siphons proportionally lengthened and protected 

 by an epidermic wrinkled sheath.* The Mya are eaten in North Britain 

 and in North America, and it is related by Fabricius that they are sought 

 after by the walrus, the arctic fox, and by various birds. 



* " This shell," remarks Dr. Gould of the Mya arenaria, " is familiar to every one who re- 

 sides on the seacoast. It is always to be seen in every market and on every quiet shore. Its 

 residence is always between high and low tide, or in such places as allow it to be partially ex- 

 posed to the ah- a part of the time. Such are our sandy beaches, muddy inlets, and mouths of 

 streams emptying iuto the sea. It usually lies just below the surface, and over it is a round 



