51 



ment may casually loosen, exhibiting the form of a 

 somewhat elevated transverse tooth." 



Very few recent species are known, and none has 

 hitherto been found in a fossil state. A fine species 

 was found at Guayaquil by Dr. M. Burrough, to 

 which I have given the name of L. inflata. 



LYONSIA HYALINA. 



SPECIFIC CHARACTER. 



Tab. XI, Jig, 2. 



Shell oblongo- ovate, extremely thin and fragile, 

 pellucid ; anterior side short, margin rounded ; pos- 

 terior side produced, slightly reflected, and trun- 

 cated at the extremity ; epidermis pale, with radiating 

 rugose striae, obsolete upon the umbones, but distinct 

 towards the base and posterior end, where the epi- 

 dermis is wrinkled ; beaks prominent. 



SYNONYME. 



Mya HYALINA, nohisy Journ. Acad. JVat, Sciences, 

 vol. 6, p. 261, pi. II y Jig. 12. 



OBSERVATIONS. 



This small species has been found abundantly in 

 Long Island sound, and on the coast of Rhode Island. 



