TABULAR SCHEME. . 69 



Cartilage in triangular cavity under each beak 

 Shell with hinder end elongated Neczra, 180-183. 

 Shell oval Poromya, 179. 



Not gaping at either end 



Ligament partly external, partly internal 

 Teeth unequal in both valves Mactra, 108-112. 

 Teeth unequal in right valve only Amphidesma, 107. 



Ligament wholly external 



Teeth two in right valve 



Inside margins notched Donax, 104-106. 



Inside margins not notched 



Teeth in left valve equal 



Shell as broad as long Lucinobsis. 122. 

 Shell not so broad as long Talina, 90-97. 



Teeth in left valve unequal Gastrana, 98. 



Teeth three in both valves 



Sinus rounded Tapes, 123-126. 

 Sinus angular Venus, 114-121. 



The bivalves being thus cleared from the path, we can take the 

 other molluscs together 



Mouth of shell without groove or canal 

 Shell multivalve Chiton, 190-200. 



Shell tubular- 

 Pointed Dentalium, 187-189. 

 Not pointed Ccecum, 453, 454. 



Shell globular Natica, 370-376. 



Shell ear-shaped 



Lip perforated Haliotis, 333. 



Lip not perforated 

 Whorls two Otina, 204. 



Whorls more than two 



Very thin and transparent 



First whorl twisted Lamellaria, 377. 



Rather thin and opaque 

 First whorl not twisted Velutina, 378, 379. 



Shell cap-shaped 



Oblong and solid, pillar fold broad Testacella, 230, 231. 

 Oblong and thin Ancylus, 205, 206. 



Beak twisted and curled 



Mouth with septum Crepidula, 384. 

 Mouth plain Capulus, 382. 



