LYON SI A. ' 29 



family. This relationship has also been remarked by 

 Carpenter in his account of the microscopical structure 

 of the shell. The mantle-tubes are united in the present 

 genus, as well as in Pandora ; they are separate in the 

 Anatinidce. Philippi considered Lyonsia to be closely 

 allied to Galeomma ; but I cannot see much resemblance 

 between them. Mr. W. "Wood was the first to notice 

 the curious appendage which coverts the hinge. It was 

 conjectured by Clark that it acted like the check- tape of 

 a trunk, to prevent its being opened too widely. This 

 might be so if it were attached to the shell. I should be 

 disposed to attribute to it quite a contrary action, and 

 to believe that its use may be to strengthen the hinge, 

 and to protect it from being squeezed too closely and 

 broken, as is frequently the case with certain species of 

 Anatina and Thracia. The ossicle of Lyonsia is of a 

 different shape and position from that of the Anatinidce. 

 In those it is semiannular, and clasps the hinge crosswise 

 with the two ends; in the present genus it is flat, and 

 lies over the hinge lengthwise, with one end at the ante- 

 rior and the other at the posterior side of it. 



This genus has several synonyms, including Maydala, 

 Leach, Osteodesma, Deshayes, and Pandorina, Scacchi. 



Lyonsia Norve'gica*", Chemnitz. 



Mya Norvegica, Chernn. Conch. Cab. x. p. 345,. 1. 170. f. 1647, 8. L. Nor- 

 vegica, F. & H. i. p. 214, pi. viii. f. 6-9, and (animal) pi. H. f. 3. 



Body milk-white, sometimes with a tinge of yellow or pale 

 brown : mantle thin ; edge studded at the anterior side with 

 from 8 to 10 papillce, which are of a darker hue in coloured 

 individuals : tubes nearly sessile ; orifice of the lower tube 

 fringed with a few short, thick, and close-set cirri ; upper 

 tube having a plain bulbous orifice, but furnished with the 



* Norwegian. 



