mQ 



MANUAL OF THE MOLLTJSCA. 



Shell omamented with rounded ribs ; beak very long, divided 

 lengthwise internally by the dental plates ; loop doubly 

 attached ? Distribution, 4 species cretaceous. Europe. Three 

 species of similar form are found in the Trias of St. Cassian. 



Magas (pumila), Sby. Eig. 153. 

 Shell smooth, conspicuously punc- 

 T- tate, dorsal valve impressed, fora- 

 men angular, deltidium rudimen- 

 tary; internal septum (s) prominent, 

 touching the ventral valve ; reflected 

 portions of the loop disunited (Z). 

 3 species. U. Green-sand — Chalk. 

 Europe. Distribution, 2 species. 

 The recent Ter. Cumingii, of New 

 but has the 



rig. 153. M. Pumila.^ 



New Zealand ; Canaries. 



Zealand, resembles Bouchardia externally, 



diverging processes of the loop as in Magas. 



Fig. 154. B. TuUpa, Bl.* 



Bouchardia (tulipa), Davidson, Eig. 164. Beak prominent, 

 \rith a minute apical foramen (/) ; deltidium blended with the 



Fig. 155. Dorsal valve. t 



shell {d) ; apophysis anchor-shaped, the septum (s) being fur- 



* The muscular impressions in Bouchardia have been compared with those of Ter. 

 Cumingii, of which the animal is known. The large impressions (r) in the disk of the 

 ventral valve appear to be formed by the cardinal muscles ; a, by the adductor ; p, by 

 tlie pedicle muscles. 



t Fig. 155. c, loop ; /, pedicle notch ; o, the ovaries. From the originals in Mr. 

 Davidson's collection ; magnified ten diameters. 



