158 



Species. 



1. anatina, Gmel. 4. nobilis, Adams. 7. truncata, Linn. 



2. arenaria, Linn. 5. praecisa, Gould. 8. Uddevallensis, Forbes. 



3. cancellata, Conr. 6. semisulcata, Adams. 



Figures. 



Mya truncata. PL Q. Pig. 5. Shell, with animal, showing at the anterior 

 end the foot, and at the posterior end the wrinkled epidermic sheath 

 enclosing the siphons. 



Mya arenaria. PI. 42. Fig. 229. Shell, showing the broadly spathu- 

 late ascending tooth. 



Genus 11. PANOPtEA, Menard. 



Animal; with the mantle closed except in front, for the passage of 

 a short stout foot ; siphons very long, more or less united at 

 their extremities, enclosed within a strong, muscular, wrinkled 

 epidermic sheath. 



Shell ; somewhat squarely oblong, equivaloe, inequilateral, gaping 

 at both e)ids ; hinge composed of a single central tooth, some- 

 times obsolete, in each valve, and a thickened fulcrum support- 

 ing a lengthened external ligament. 



Panopma is a large bivalve, the largest of bivalves excepting the colos- 

 sal Clams of the family Tridacnacea, of similar structure and of the same 

 mud-dwelling habits as Mya ; but the shell, though bearing a general re- 

 semblance to that of Mya, has more the hinge of Solen,the ligament being 

 external, supported by a thickened fulcrum. While speaking of the Ce- 

 p/talopods (ante, vol. i. p. xi.) I remarked that the Nautilus and Spirula 

 are the solitary living remnants of a numerous extinct race of mollusks, 

 represented by the fossil Ammonites ; the Panopaa presents a similar 

 history. Nearly a hundred and forty species are known in a fossil state, 

 occurring in every part of the world where secondary or tertiary strata have 

 been found, but of living species we have only eleven, all of more or less 

 rarity, and some of them very imperfectly known. The animal has not 

 been met with until lately. About twenty-two years back, " the officers 



hole through which the animal ejects a jet of water to a considerable height above the sand ; and 

 if the shallow water is observed where they are known to dwell, it will be perceived to be kept 

 in constant eddies by the suction and ejection of the water. It is valuable as an article of food, 

 in the fisheries, and for manure." — Invert. Massachusetts, p. 41. 



