168 MYTILID®. 
ting strie ; hinge margin crenulated behind the ligament ; interior bril- 
hantly nacreous. 
C. impacta, Hermann; Reeve, Conch. Le (Modtola,) f. 64; C. 
discors, Lamark, viu., p. 23; Chenu, f. 753. Oval, sub-diaphanous, the 
extremities radiately ribbed, and the middle finely longitudinally 
striated ; brown, with sometimes a mixture of green near the edge ; 
inside highly iridescent. 
Height, °85; length, 1-3. 
Common. Auckland to Dunedin. Chatham Islands. Europe. 
North America. 
Genus, MODIOLA—Lamark. 
Margin of mantle simple, open ; anal tube short, more or less per- 
fect. Shell oblong, inflated in front ; umbones anterior, obtuse ; hinge 
toothless ; pedal impressions three in each valve, the central elongated ; 
epidermis often produced into long beard-like fringes. 
M. australis, Gray; Sowerby in Conch. Ic., f. 21. Shell ovately 
fan-shaped ; posterior side very short; anterior broadly dilated, convex 
in the middle, concentrically striated; yellowish chestnut, sparingly 
bearded towards the margin (Sowerby.) 
Stewart Island. Austrailia. 
M. areolata, Gould, U.S., Ex. Ep.,xii., p. 452, f 562. Smooth, 
swollen ; covered with chestnut-brown hairy epidermis, under which it is 
pinkish ; inside yellowish-white, getting purplish behind. 
Meioht 115; length, 2. 
Common. Chatham Islands. Auckland Islands. 
The Natives call this shell ‘‘ purewha.” 
Probably identical with the last. 
M. fluviatilis, “ucton, Jour. de Conch., 1866, ~. 53. Smooth, 
finely concentrically striated ; epidermis smooth, brownish-black, under 
which it is purple ; inside bluish-white, purplish round the margin. 
Height, “5 lengthy or. 
Great Lagoon, Chatham Islands. Dunedin. In brackish water. 
Sub-Family—Lithodomine. 
Hinder part of mantle more or less produced ; anterior adductor 
muscle moderate. 
Genus, LITHODOMUS—Cuvier. 
Shell oblong, cylindrical, extremities rounded, covered with a thick 
epidermis ; hinge linear without teeth; lgament marginal, internal ; 
interior nacreous ; boring in stones. 
L. truncatus, Gray, Dief. N.Z,, ii, p. 259. Reeve, Conch. Ic., f 
3; Voy. Erebus and Terror, Moll., pl. 2, f. 12. Shell oblong, sub-cylin- 
