KXPLANATION OF I'LATF XXVIII. 



FK;U:E 201. Cyprina Islandica, (p. GSIJ ;) iiatural si/c. 

 202. Mactra solidissima, (p. 630;) natural size. 



(The figures are I>ot1i from Himiry's r.oul.l. drawn l>y Y.. S. Morse.. 



