174 



22. spatha, Jeffr. 24. subericola, Macg. 25. truncata, Qualr. 



23. Stutckburyi, Blain. 



Figure. 



Teredo marina. PI. 46. Fig. 248. Shell, showing the posterior aper- 

 ture through the large anterior aperture, with the slender inner 

 apophyses. Above is the shelly tube. 



Genus 2. GASTROCILENA, Spengler. 



Animal ; cuneiform, or, when the siphons, which are separated only 

 at their extremities, are extended, elongated ; orifices fringed ; 

 mantle closed, and thickened where exposed, with a very small 

 opening for the small pointed curved finger-shaped foot, which 

 sometimes spins a delicate byssus. (Forbes. J 



Shell ; ovately or elongately wedge-shaped, equivalve, largely gaping 

 anteriorly ; hinge toothless, but furnished with a small spathu- 

 late lamina and an external ligament ; tube calcareous, club- 

 shaped, free or attached, often incomplete. 



Gastrochcena is a genus of thirty species distributed in all parts of the 

 world, combining the organization of two very distinct though nearly 

 allied families. The animal is like that of Saxicava and Petricola rather 

 than of Pholas, having only a small finger-shaped foot, and a shell whose 

 valves are connected by a regular external ligament ; but the shell largely 

 gapes in front, and the animal, with its mantle thickened where exposed, 

 is not only a borer, but has the faculty of constructing for its place of 

 habitation an elongately club-shaped, or a rude flask-shaped, sheath. How 

 this is effected has never yet been satisfactorily shown. The sheath, ex- 

 cept in G. mumia (Fistulana clava, Lamarck), appears to offer few cha- 

 racters peculiar to the species, — few, that is to say, which vary with the 

 variations of the shell ; but there are not many species of which the tube 

 has been observed. It is sometimes free, sometimes attached to shells or 

 stones, sometimes it is incomplete ; and when the creature makes for itself 

 a cavity in madrepore or other substance, it lines the walls with shelly 

 matter and the sheath is dispensed with altogether. More observations 

 are needed of the exotic species of this very interesting mollusk before ge- 

 neralizing further upon its habits. 



