EXPLANATION OF PLATE XXVII. 
FiGtre 186.—Teredo navalis, (p. 669;) shell and pallets. 
187.—Teredo Thomsoni, (p. 670;) shell and pallets. 
188.—Teredo megotara, (p. 670;) shell and pallets." 
189.—Xylotrya fimbriata, (p. 670;) shell and pallets. 
190.—Gastranella tumida, (p. 678;) shell, enlarged six diameters. 
191.—Corbula contracta, (p. 672;) natural size. 
192.—Saxicava arctica, (p. 671;) natural size. 
193.—Clidiophora trilineata, (p. 673;) natural size, with animal. 
194,—Lyonsia hyalina, (p. 672;) natural size. 
195.—Thracia truncata, (p. 674;) natural size. 
196.—Thracia myopsis, (p. 673;) natural size. 
197.—Periploma papyracea, (p. 673;) natural size. 
198.—Cochlodesma Leanum, (p. 673;) natural size. 
199.—Petricola pholadiformis, (p. 680 ;) natural size. 
200.—Pholas truncata, (p. 670 ;) natural size. 
. Saeed 190 was drawn by A. E. Verrill; all the rest are from Binney's Gould, mostly drawn by E. 
S. Morse. 
