274 THE LAMELLIBRANCHIA 
closed ; siphons long and united throughout their length; a fourth 
opisthopodial pallial aperture. Foot rather large, compressed. Shell 
elongated, with a deep pallial sinus and a spoon-shaped projection for the 
ligament on each valve. Genera—Lutraria, Lamarck ; British. T'resus, 
Gray. Standella, Gray. Famity 5. Sonenmpar, Leach. Elongated, 
burrowing animals. The foot more or less cylindrical and powerful, 
without a byssus. Gills narrow. Shell long, truncated, and gaping at 
each end ; the ligament external. Genera—Solenocurtus, de Blainville ; 
siphons large, partially united, incompletely retractile ; pallial sinus deep ; 
foot very large and linguiform (Fig. 194); British. Tagelus, Gray ; 
posterior extremity short ; pallial sinus very deep ; estuarine. Ceratzsolen, 
Forbes and Hanley; siphons long, separate ; gills rather short and not 
folded ; British. Cultellus, Schumacher ; siphons rather short ; extremity 
of foot dilated ; British. Stliqua, Megerle ; siphons of medium length ; 
foot dilated; shell compressed. olen, Linnaeus; siphons short; foot 
elongated ; shell rectilinear, cylindrical; the umbones anterior and 
terminal ; British. Hnsis, Schumacher ; siphons very 
short ; a fourth pallial orifice ; shell arcuate, the um- 
bones anterior and sub-terminal ; British. Famity 6. 
SaxIcavipAk, Gray. Mantle extensively closed ; with 
a small pedal orifice (Fig. 246, f) ; siphons elongate, 
covered by a chitinous sheath and wholly or largely 
united ; gills prolonged into the branchial siphon. 
Foot small. Shell gaping, with an external ligament. 
ok Genera—Saxicava, Fleuriau ; bores holes in rocks ; 
siphons free at their extremities; foot byssiferous ; 
British (Fig. 246). Glycimeris, Lamarck ; siphons 
very long and completely united ; a burrowing form. 
Cyrtoduria, Daudin ; shell inequilateral ; the anterior 
buy ~ a6 side the longer ; siphons united, incompletely retractile. 
Fic. 246. FamMity 7. GASTROCHAENIDAE, Gray. Shell thin, 
Savicava arctica, ven. Without teeth, gaping widely at the anterior end. 
tral aspect. a.s, anal Anterior adductor much reduced. Foot small and 
siphon ; br.s, branchial 
siphon; by, byssal without a byssus. Gills narrow. Mantle extensively 
antes ele P% closed ; with long united siphons. Genera—Gastro- 
chaena, Spengler ; a boring form, with a cylindrical 
foot ; the shell regular and rarely enclosed in an adventitious tube ; 
British.  Fistulana, Bruguitre ; a burrowing form with a very small 
compressed foot; shell with a denticulate border, always enclosed in a 
regular, non-adherent, fragile, club-shaped adventitious tube. 
Sup-ORDER 8. ADESMACEA. 
Eulamellibranchia with very long united siphons and a largely 
closed mantle. The foot short, truncated, discoid, and without a 
byssus. The gills prolonged into the branchial siphon. The shell gaping 
and devoid of a ligament, but with a styloid apophysis in the umbonal 
cavities. 
Famity 1. PHontapimpaAr, Adams. Shell capable of containing all 
