500 



MOLLUSCA 



PHYLUM VI 



yoiing, boriiig in the softer rocks. Tertiary and Recent. Subgenus Panomya Gray 

 {Chaenopea Mayer). 



Panope Menard ^ {Glycimeris Lam. 1799, non Da Costa) (Fig. 830). Large, gaping 

 widely behind and sliglitly in front ; siirface concentrically, or feebly sculptured ; an 

 obscnre tootli in eacli valve. Cretaceous to Recent. 



Gyrtodaria Daudin (Glycimeris Lam. 1801, non. Schum.). Solenoid witli strong 

 epidermis. Pliocene and Recent. 



Family 44. Gastrochaenidae Gray. 



Shell suhstance as in Saxicava ; valves equal, widely gaping in front ; adductor scars 

 unequal, the anterior smaller ; pallial sinus deep, margins simple ; area none ; ligament 

 and resiliurn external, parivincular ; hinge with a single obsolete cardinal or wholly 



edentulous ; animal frequently forming 

 an external protective tuhe to Supplement 

 its hurrow, hut to which it is in no way 

 attached. (?) Permian. Trias to Recent. 



This group Stands between the Myacea 



and Adesmacea, verging on the latter. Many 



of its characters are adaptive, and are re- 



peated in the Ensiphonacea, but niorpho- 



c»^™=e. mS l°gi'=='"y it« ■■•'l'^ttons to the Saxicavidae 



- - seem close. 



Fio. 832. 

 Gastrochaena deslong- 



Fio. 831. 



Gastrochaena angusta Desh 

 Eocene (Sables moyens) 

 Valmandois, near Paris. 



Jura; Baiin, near Cracow 

 Internal mould of burrow 

 including one of the 

 valves, i/j. 



Gastrochaena Spengler ( Ghaena 



Retzius ; Rocellaria Blainv.) (Figs. 831, 



832). Bores cylindrical or pear-shaped cavities in rock, sliell, or coral. Trias to Recent, 



Fistulana Brug. Secretes calcareous tiibes wliich stand upriglit in the sand or 



mud. Recent. 



Superfamily 17. ADESMACEA Blainville. 



Gills with direct and reßected laminae, long, united, extended into the hranchial 

 siphon ; posterior adductor usually in front of the visceral ganglion, anterior adductor 

 external to the cavity of the valves, exerted in a contrary sense to the posterior muscle ; 

 hinge margin reflected, edentulous ; ligament obsolete ; a myophoric process extending 

 freely into the valve from the sub-umbonal cavity. 



Family 45. Pholadidae Fischer. 



Shell cellulo-crystalline, with a thin epidermis ; valves more or less gaping in front 

 and behind, with inconspicuous beahs and reticulate, often spinöse sculpture ; in the 



Fig. 833. 

 Fholas levesquei Watelet. Eocene ; Ciiise de la Mothc 



adult supplemented by accessory shelly pieces, always attached to the valves, but rarely by 

 an exterior shelly tube like that of the Gastrochaenidae ; the antero-dorsal margins more 

 or less extensively reßected, the postero-ventral approximated ; pallial line sinuated, area 



^ Erroneously written Panopea by many authors. 



