Dosinia.] PELEC'YPODA. 975 



SUBORDER 4. VENERACEA. 



Eulamcllibranchia with 2 pa Ilia 1 sutures ; the siphons generally 

 somewhat elongated and partially or wholly united. Gills normal, 

 united to form a complete anal chamber. Adductor muscles subequal. 



Shell-substance densely cellule-crystalline, with inconspicuous epi- 

 dermis ; ligament external, parivincular, seated in a groove. 



Fam. VENERID^E, Lwu-h. 



Animal having the mantle widely open in front for the passage of 

 the foot, which is well developed ; siphons variable in length, free or 

 partly united, orifices distinct and fringed ; foot linguiform, com- 

 pressed, rarely byssiferous ; adductor muscles subequal. 



Valves equal, free, closed, with prosogyrous beaks, variably sculp- 

 tured, with the margins more or less dentate, except in the smooth 

 species ; adductor-scars peripheral, pedal distant ; pallia! sinus more 

 or less sinuated, area very distinct ; resilium usually external, em- 

 braced by the ligament ; hinge-plate developed, with 3 cardinals in 

 each valve and a single obsolete lateral in one valve ; the cardinals 

 frequently bifid, usually radially disposed and subequal in size, except 

 the posterior left one, which is often obsolete or obscure ; supple- 

 mentary cardinals or rugosities are present in specialized forms. 



This family corresponds to the Conques marines of Lamarck. 



Jura to Recent, the maximum in the Tertiary and later. 



Subfam. 1. DOSINIIN^E. 



Hinge with 3 left and 3 or 4 right cardinals, usually with an 

 anterior left lateral fitting into a pit in the opposite valve and some- 

 times a developed posterior right lateral. 



Siphons long and united to their tips ; foot large, arcuate, with- 

 out a byssus or byssal groove. 



Shell usually orbicular and generally more or less compressed, 

 with a distinct pallial sinus. 



Genus 1. DOSINIA, Scopoli, 1777. 



Dosinia, Scopoli, Introd. Hist. Nat., 1777, 399. Cythcrea, Bolten, 1798. 

 Orbiculus /3, Hegerle, 1811. Arthemis, Oken, 1815. Artemis, Conrad. 

 1832. Asa, Defrance, 1825. Arctoe, Risso, 1826. Exoleta, Brown, 1827. 

 Arctoa, Herrrnansen, 1846. Cerana, Gistel, 1848. Assa, Gray, 1851. 

 AmphithcEa, Leach, 1852. Not Dosinia, Gray, 1838, and P.Z.8., 1847. 

 Type : Dosinia africana, Hanley. 



Animal with plicated and anteriorly papillate mantle-borders ; 

 siphons very long and closely united ; branchial orifice with a few 

 sessile papillae, anal orifice undulated ; labial palpi small, triangular ; 

 gills very unequal, the outer short and appendiculate ; foot large, 

 arcuate, no trace of a byssiferous gland. 



Shell orbicular, generally compressed, with a long and strong 

 ligament seated in a groove and enfolding a heavy resilium ; lunule 



