68 TABULAR SCHEME. 



Ligament conspicuous 



Rising above level of dorsal line -Cyamium, 49. 

 Partially overlapped in a groove 



Anterior scar narrow and projecting far within 



pallial line Lucina, 61, 62. 

 Shell thick, large and heavy, scars oval and 

 shiny Cyprina, 53. 



Ligament inconspicuous, shell horny and trans- 

 lucent 



Beak at fore end Pisidium, 85-89. 

 Beak midway Sphcerium, 81-84. 



C. Pallial line indented, siphons long 



Shell inequivalve 



Nearly equilateral, ligament in internal groove Lyonsia, 



I 73- 



Elongated at hinder end Pandora, 172. 



Truncated at hinder end 



Hinge with ossicle Thracia, 174-178. 

 Hinge without ossicle, cartilage in cavity of cardinal 

 C orb i' la, 146. 



Shell equivalve 



Gaping at both ends 



Shell long and narrow 



Hinge nearly midway, with radiating ribs Cerati- 



solen, 151. 

 Hinge terminal, one cardinal in right valve Solcn , 



I52-I55- 



Hinge sub-terminal, two cardinals in right valve 



Solecurtus, 149, 150. 



Shell oblong and very oblique Lutraria, 147, 148. 

 Shell broad with a broad, short shelf Mya, 7. 

 Gaping posteriorly 



Beaks turned towards hinder end Scrobicttlaria, 



99-103. 

 Shell striated radially and concentrically Psammobia, 



139-142. 



Shell with long, calcareous sheath Gasti'ochcena, 159. 

 Shell with wrinkled periostracum extending over 



siphons Mya (as regards binghami, 145). 

 Shell elongated, thin and prickly Petricola, 128. 

 Shell with thin, concentric plates Venerupis, 127. 



Shell obliquely truncated at hinder end 

 Pallial line continuous Panopcea, 158. 

 Pallial line broken up-*-Saxicava, 156, 157. 



