882 PELECYPODA. [Eulamellibranchia. 



Shell degenerate, sessile, inequivalve, generally edentulous, wings 

 obsolete ; with a subnacreous or porcellanous inner and prismatic 

 outer layer ; epidermis inconspicuous ; area amphidetic, ligament 

 alivincular. 



Fam. LIMID^, d'Orbigny. 



Animal with a digitiform foot with a byssogenous apparatus. 

 Borders of the mantle provided with long and numerous tentacles. 

 Gills not united with the mantle, with direct and reflected limbs. 



Shell equivalve or subequivalve, auriculate, gaping, free or fixed 

 by a byssus ; beaks pointed, straight, distant, showing part of the 

 area and of the ligamental fossette between them ; hinge edentulous, 

 or with traces of denticles on each side of the resilifer ; area amphi- 

 detic, equal in both valves ; ligament alivincular, resilium subinternal. 



Carboniferous to Kecent. 



Genus 1. LIMA (Bruguiere), Cuvier, 1798. 



Lima, Bruguiere, Enc. Meth., 1792, pi. 206 ; Cuvier, Tabl. Elem., 1798, 421. 

 Type : Ostren lima, L. Mantdlum. Bolten, Mus. Bolten., 1798, 1HO. 

 Limaria, Link, Beschr. Rostock Samml., 157. (tlnut-ion. Oken, ZooL, 

 1815. Radula, H. and A. Adams, Ad. G.R.AL, ii, 1858, 556; not of 

 Gray, 1844. Ctenoides, H. and A. Adams, I.e., 557. Acesta, H. and A. 

 Adams, i.e., 558. 



Animal with the outer border of the mantle beset with rows of 

 unequal long tentacles ; duplication of the inner border of the mantle 

 free floating, the ocelli not easily visible ; foot digitiform, canaliculate ; 

 byssus more or less developed ; lips ornamented with arborescent out- 

 growths ; labial palps small, striated on the inner side ; rectum float- 

 ing at the posterior end of the adductor of the valves. 



Shell equivalve, compressed, white, obliquely oval, having rayed 

 ribs or striae, auriculate ; anterior side generally straight, gaping ; 

 posterior side rounded, usually closed ; hinge area triangular, with 

 a central resilium ; muscular impressions lateral, duplex, large. 



Distribution. All seas. 



Fossil in the Secondary and Tertiary, the maximum in the Cre- 

 taceous. 



Vernacular Name. File-shell. 



Remarks. The Limas appeared in very ancient epochs, and during 

 the Oolitic period species were comparatively abundant and attained 

 great dimensions. About thirty well-marked forms inhabit existing 

 seas, living in various depths of water, either free, or moored by a 

 byssus, or enveloped in nests formed of byssal filaments. 



The animals are very beautiful and curious, and often much larger 

 than their shells, which in the greater number of species, though 

 remarkable for elegance of outline and sculpture, rarely present any 

 other colour than a milky-white. The majority of known living 

 species come from the South Seas and Indian Ocean. 



