302 anatinidjE. 



S])ecies of Penploma. 



argentaria, Conr. lenticularis, Sow. 



angulifera, Phil. ovata, D'Orb. 



insequivalvis, Schurn. planiuscula, Soiv. 



Leana, Conrad. prsetenuis, Pultn. 



Genus LYONSIA, Turton. 



Siphons short, separate at their extremities. 



Shell thin, iuequivalve, more or less inequilateral, trun- 

 cate and somewhat gaping posteriorly, hoth valves convex, 

 the left the larger, surface often striated and invested with 

 an epidermis, interior sub -nacreous. Hinge composed of 

 an oblique cartilage-plate in each valve ; cartilage internal, 

 covered iu front, with a flat oblong ossicle. Muscular and 

 pallial impressions faint, the latter sinuated. 



Syn. Magdala, Leach. Hiatella, Myatella, Brown. 

 Tetragonostea, Osteoderma, Desk. Pandorina, Scacchi. 



Ex. L. Norvegica, Chemnitz, pi. 96, fig. 3. Shell, L. 

 Norvegica, fig. 3, a, 3, b. 



The palpi in Lyonsia are triangular and narrow, the 

 orifices of the short, united siphons are fringed, and the 

 linguiform, compressed foot is furnished with a byssal 

 groove. The Entodesma of Philippi, from the Island of 

 Chiloe, does not appear from his description to differ 

 materially from Lyonsia. The extinct genera, Ceromya 

 and Gresslya of Agassiz are also very closely allied to this 

 genus, but there is a lamina behind the beaks and within 

 the posterior hinge-margin. In their geographical distri- 

 bution the species of Lyonsia range from the shores of 

 Greenland and Norway to those of India and South 



