MACTRIDA. 159 
(six miles), is made of Gnathodon shells procured from the east 
end of the lake, where there is a mound of them a mile long, 
fifteen feet high, and twenty to sixty yards wide; in some places 
it is twenty feet above the level of the lake—Ly&.u. 
RANGIANELLA, Conr., 1867. Lateral teeth straight, subequal, 
not elongated, entire. The only sp. is R. trigona, Petit. 
PERISSODON, Conrad. PP. clathrodonta, Conr. Miocene. 
SuBFAMILY LUTRARIINZ. 
Shell usually oblong or elongated, sometimes oval, gaping 
behind ; lateral teeth very small, rudimentary, sometimes obso- 
lete, and especially in adult or old shells. 
Lurraria, Lamarck, 1799. 
Otter’s-shell. 
Syn.—Mactra (partim), Linn. Lutricola (partim), Blainv. 
Psammophila, Leach, 1827. 
Distr.—33 sp. United States, Brazil, Britain, Mediterranean, 
Senegal, Cape, India, New Zealand, Sitka. Fossil. Tertiary—; 
United States, Europe. ZL. oblonga, Gmel. (cix, 8). 
Shell oblong, gaping at both ends; cartilage-plate prominent, 
with 1 or 2 small teeth in front of it, in each valve; pallial sinus 
deep, horizontal. 
Animal with closed mantle-lobes ; pedal opening moderate ; 
foot rather large,compressed ; siphons united,elongated, invested 
with epidermis ; palpi rather narrow, their margins plain ; gills 
tapering to the mouth. 
Resembles Mya; burying vertically in sand or mud, especially 
of estuaries ; low-water to 12 fathoms. JL. rugosa, found living 
on the coasts of Portugal and Mogador, is fossil on the coast of 
Sussex, England. 
DARINA, Gray, 1849. Shell oblong, compressed, rounded and 
a little gaping at each extremity; beaks subposterior; hinge 
with a large, spoon-shaped pit; lateral teeth very small, con- 
founded with the cardinal tooth. Ligament separated from the 
pit by a lamella. L. Solenoides, King (cix, 9). 
ZENATIA, Gray, 1849. (Metabola, Mayer.) Shell oblong, 
elongated, compressed; beaks not prominent, anterior, close ; 
cardinal teeth distinct ; lateral teeth none ; ligament subexternal, 
marginal, not separated from the cartilage. LZ. acinacies, Quoy 
ex, 11); 
CHCELLA, Gray, 1849. Shell oblong, subequilateral ; cardinal 
tooth of the left valve large, triangular ; lateral teeth very nar- 
row, contiguous to the cardinal tooth; cartilage-pit projecting ; 
ligament marginal. L. turgida, Desh. (ex, 12). 
VANGANELLA, Gray, 1849. (Resania, Gray, 1849. Laminaria, 
Mayer. Myomactra, Mayer.) Valves with two interior diver- 
