606 



MANUAL OF THE MOLLTISCA. 



Shell ornamented with rounded ribs ; beak very long, dividetl 

 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. Fig. 153. 

 Shell smooth, conspicuously j)unc- 

 Z tate, dorsal valve impressed, fora- 

 men angular, deltidium rudimen- 

 tary; internal septum (.s) prominent, 

 touching the ventral valve ; reflected 

 portions of the loop disunited {I). 

 3 species. U. Green-sand — Chalk. 

 Europe. Distribution, 2 species. 

 New Zealand ; Canaries. The recent Ter. Cumingii, of New 

 Zealand, resembles Bouchardia externally, but has the 

 diverging processes of the loop as in Magas, 



Fig. lo3. M. Pumila. I 



Fig. 154. B. Tulipa, Bl.* 



Bouchardia (tulipa), Davidson, Fig. 154. Beak prominent, 

 with a minute aj)ical foramen (/) ; deltidium blended with the 



Animal. Jy Fig. 155. Dorsal valve. t 



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



* The rauscular 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 tlie 

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

 the pedicle muscles. 



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

 Davidson'? collection ; magnified ten diameters. 



