Shell. Oval or elongated, regular, equivalve, more or less inequilateral, sometimes but slightly gaping: edges always simple and trenchant; summits feebly marked; hinge subsimilar, formed by two very small divergent cardinal teeth; two very distinct muscular impressions united by a palleal impression profoundly sineous to the rear. Inhabits the seas of Europe and America. Fourteen species.
- Lutraria solenoides.
- L. rugosa.
- L. compressa.
- L. piperata.
- L. tellinoides.
- L. candida.
- L. elliptica.
- L. papyracea.
- L. plicatella.
- L. crassiplica.
- L. complanata.
- · · · · ·
- L. lineata.*
- L. Nuttallii.*
- L. caniculata.*
2. Genus Mactra. Pl. [VI].
Animal. Body oval and pretty thick; edges of the mantle thick, smooth, or without tentacular papillæ, augmented behind by two indistinct tubes; mouth small and oval; labial appendages narrow; branchial laminæ very small, and united in their length among themselves and with those of the opposite side; foot oval, trenchant, very long.
Shell. The Mactra has a peculiar hinge distinguishing it from all other genera. It is triangular, with a curved or angular compressed tooth on each valve, with a small oblique cavity on each side, to which is attached the ligament. Two lateral teeth, one near the primary tooth and one near the ligament. The shape of the shell is subtriangular or oblong; exterior smooth, striated, or ribbed transversely; two muscular impressions united by a narrow marginal tongue. Inhabits the British and American coasts. Forty-four species.
- Mactra spengleri.
- M. striatella.
- M. carinata.
- M. straminea.
- M. Australis.
- M. violacea.
- M. fasciata.
- M. turgida.
- M. plicataria
- M. rufescens.
- M. maculata.
- M. subplicata.
- M. triangularis.
- M. lactea.
- M. abbreviata.
- M. crassatella.
- M. helvacea.
- M. grandis.
- M. stultorum.
- M. maculosa.
- M. ovalina.
- M. castanea.
- M. rufa.
- M. squalida.
- M. brasiliana.
- M. donacina.
- M. depressa.
- M. lilacea.
- M. trigonella.
- M. deltoides.
- M. alata.
- · · · · ·
- M. gigantea.*
- M. solida.*
- M. oblonga.*
- M. californica.*
- M. arctata.*
- M. nucleus.*
- M. alba.*
- M. similis.*
- M. fragilis.*
- M. lateralis.*
- M. deaurata.*
- M. planulata.*
- M. tellinoides.*
3. Genus Crassatella. Pl. [VI].
Animal. Unknown.
Shell. Close, suborbicular or transverse, striated longitudinally, denticulated, regular, equivalve, inequilateral, summits well marked, and turned to the front: primary teeth somewhat divergent with a hollow at the side; no lateral teeth nor obsolete ones; ligament internal and inserted into a pit in the hinge. It is easily known from the Mactra and Lutraria by the valves fitting exactly. The living species of this genus only exist in the seas of Australasia, while in a fossil state we find at least seven species in France. Eleven species.
- Crassatella kingicola.
- C. donacina.
- C. sulcata.
- C. rostrata.
- C. glabrata.
- C. subradiata.
- C. contraria.
- C. cuneata.
- C. Erycinæa.
- C. cycladea.
- C. striata.