112 PEOVISIONAL AID TO THE STUDY OF TASMANIA!* MOLLUSCA. 



margin smooth or denticulated ; pallial line simple ; 

 hinge-teeth 12, striated in front of cartilage-pit; 

 lateral teeth — 1, 1—0; adductor impressions deep, 

 rounded ; pedal small, distinct. Dist. — Australia, New- 

 Zealand, Philippines, India, West Africa, Canaries, 

 Brazil. 



(lxxxix.) Family Astaetid^:. 

 Shell thick, solid, equivalve, the cardinal teeth always well 

 developed, 2—3 in each valve ; lateral teeth some- 

 times present on one or both sides, ligament always 

 external, strong ; muscular scars ovate, the anterior 

 usually with a small deep superimposed pit, produced 

 by the retractile muscles of the foot ; pallial line 

 entire. 



Genus Caedita. (665-668.) 

 Shell oblong, radiately ribbed ; ligament external ; margins 

 toothed; hinge-teeth T2, and an elongated posterior 

 tooth; pallid line simple; anterior pedal scar- close to 

 adductor. Dist. — Universal. 



Genus Mytilicaedia. (669-670.) 

 Shell elongated, very inequilateral, with squamous radiating ribs ; 

 hinge with an anterior triangular cardinal tooth ; 

 posterior cardinal tooth double in the left valve ; no 

 anterior laterals. Foot rounded, grooved, byssiferous. 

 Dist. — Universal. 



,( xe -) Family Unionid^i. 

 Genus Unio. (671.) 

 Shell nacreous; epidermis thick and dark, oval or elongated, smooth, 

 corrugated, or spiny, becoming very solid with age ; 

 anterior teeth 1-2, or 2-2, short, irregular; posteror 

 teeth, 1-2, elongated, laminar. Dist. — Fresh water. 

 Universal. 



(xci.) Family Teigoniid^. 

 Genus Teigonia. (672.J 

 Shell trigonal, nacreous internally, thick, tuberculated or 

 ornamented with radiating or concentric ribs ; posterior 

 side angular ; ligament small and prominent ; hinge- 

 teeth 2-3, diverging, transversely striated; centre tooth of 

 left valve divided; pedal impressions in front of the 

 posterior adductor, and one in the umbo of the left 

 valve ; anterior adductor impression close to the 

 umbo ; pallial line simple. Dist. — Australia. 



