127 



long, ligulate, byssiferous, perforate, projecting from an anterior 

 opening in the mantle. (Forbes.) 

 Shell ; small, thin, oblong-oval, equivalce, moderately inequilateral ; 

 a sinale cardinal tooth in each valve, and these sometimes want- 

 ing ; ligament part internal, part external. 



The little transparent bivalves known as Galeommce, and of which we 

 have an interesting example in G. Turtoni of the Channel Islands and the 

 western Mediterranean, do not properly belong to the family of the Nym* 

 pliacea, but until something more is known of their characters than at pre- 

 sent, the genus cannot be appropriated with any certainty. Messrs. Forbes 

 and Hanley consider it to be the nearest allied to Area, Dr. Gray to Solemya 

 and Pandora, M. Mittre to Tridacna, Costa to Gastrochcena, and amid 

 these conflicting opinions formed on the investigation of the same species 

 it would be better to wait until the animals of some of the foreign species 

 have been examined. 



Galeomma differs from Tellina very conspicuously in having the mantle- 

 margins closed, with only an opening for the passage of the foot, and in 

 the foot being byssiferous ; the siphonal orifices are not tubular ; and the 

 shell which gapes at the ventral margin is almost, if not altogether tooth- 

 less, the valves being connected by a ligament, which is partially if not al- 

 together internal. The shell is moreover covered with a transparent horny 

 skin, which Mr. Alder describes as being composed of two layers, the lower 

 of which is slightly muscular, whilst the outer is granular and covered with 

 tubercles, which possibly, when the animal is alive, may rise into papillae. 



The Lamarckian Psammobia aurantia, a native of the Mauritius, is con- 

 sidered to belong to the genus, and a few other species have been added. 



1. ainbigtta, Desk. 



2. angusta, id. 



3. argentea, id. 



4. aurantia, Lam. 



5. cliloroleuca, Desk. 



Species. 



6. formosa, Desk. 



7. iiulecora, id. 



8. inflata, id. 



9. Layardi, id. 



10. macrochisma, id. 



11. paucistriata, Desk. 



12. polita, id. 



13. splendida, id. 

 H. Turtoni, Sow. 



Figures. 



Galeomma Turtoni. Plate P. Shell enlarged and widely opened, as in 

 our figure of Tridacna, to show the animal with the mantle closed, 

 and having an opening for the passage of the foot. 



