MOLL USCA—PELECYPODA . 371 



i3 n . Shell thicker, not perforate h f/ . 



h". Byssal opening prominent J /// - 



j /// . Beak minute, strongly inflected. 



LIII. Honeoyea. 

 3 f,/ . Beak not minute, very slightly inflected. 



LI. Lunulicardium. 



h". Byssal opening absent CLXVII. Linearia. 



ww. Shell semicircular LXXIV. Halobia. 



ww. Shell subcircular 2 1 f. 



2if. Shell exceedingly thin ; lower valve flat and perforate near 



the umbo for the byssus CVII. Paranomia. 



2 1 f . Shell of medium thickness 1 8*. 



1 8*. Beaks prominent I 4 / '- 



14" , Both anterior and posterior lateral teeth present.. .z y/ . 



i ff . Ribs over entire shell CLVII. Cardium. 



i n '. Ribs only on posterior part of shell. 



CLVIII. Protocardia. 



14" '. No lateral teeth present CXLIV. Venericardia. 



18*. Beaks not prominent ; cardinal teeth three in each valve. 



CXLI. Ptychomya. 



ww. Shell oval CLXVII. Linearia. 



666. Surface not marked with radial ribs, though radiating striae may be 



present xx. 



xx. Shell elongate laterally 22f. 



22f. Greatest length of shell parallel with the long, straight hinge 



line 19*. 



19*. Beaks terminal or practically so..CXXXI. Pleurophorus. 



19*. Beaks varying from subcentral to anterior I S // - 



15" . An internal rib present, running from beak to base./ 7 '. 

 j // . Left valve with two cardinal teeth. 



CLXXI. Siliqua. 

 j". Left valve with one cardinal tooth. 



CLXXII. Leptosolen. 



iS // - No internal rib present CLXXIV. Legunien. 



22f . Greatest length of shell parallel with the long, arcuate hinge 



line, unioid 20*. 



20*. Shell with a small, anterior lobe 16". 



i6 // . Umbonal ridge present LXXXIV. Anthracomya. 



16". No umbonal ridge LXXXIII. Naiadites. 



20*. Shell without a small anterior lobe if '. 



iy // . Cardinal teeth present k f/ . 



k". Cardinals small, several, coalescent. 



LXXXV. Nyassa. 

 k n ' . Cardinals one or two, large, heavy. 



LXXXVI. Unio. 



ij n '. Cardinal teeth absent / /r . 



I". Lateral teeth absent LXXXVII. Anodonta. 



l n ' . Lateral teeth represented by one or two folds. 



LXXXII. Amnigenia. 



22f . Greatest length of shell at about 45 to hinge line 21*. 



21*. Beaks prominent, terminal, elongate i8 ff . 



