MACTRID^. 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 j^ards wide ; in some places 

 it is twent}'^ feet above the level of the lake. — Lyell. 



RANGiANELLA, Conr., 1867. Lateral teeth straight, subequal, 

 not elongated, entire. The only sp. is R. trigona, Petit. 



PERissoDON, Conrad. P. clathrodojita, Conr. Miocene. 



Subfamily LUTRARIIN^. 



Shell usually oblong or elongated, sometimes oval, gayjing 

 behind; lateral teeth very small, rudimentary, sometimes obso- 

 lete, and especially in adult or old shells. 



LuTRARiA, 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. L. 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. L. rugosa, found living 

 on the coasts of Portugal and Mogador, is fossil on the coast of 

 Sussex, England. 



DARTNA, 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. L. acinacies^ Quoy 

 (ex, 11). 



c^CELLA, Gray, 1849. Shell oblong, subequilateral ; cardinal 

 tooth of the left valve large, triangular ; lateral teeth ver^^ 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- 



