CONCHOLOGY. 
Includes Mytilus Tulipa, Modiolus, Gibs:, 
discors, and discrepans. 
40. Lima. Shell longitudinal, oblong, equivaive, 
inequilateral, with auricles at the base, and the 
beaks rather remote. Teeth none, but under the 
beaks is an external cavity and a transverse 
dissepiment. 
Includes the Ostrea fragilis and subauriculata. 
41. Aviculu, Shell flat, cblique, inequivalve, ine. 
quilateral, transversely produced in a_ siraight 
line at the base, where the sides are lobed; the 
beaks rather remote. Hinge linear, with a sing!le 
slightly penetrating tooth : lateral teeth none. 
Includes the Mytilus Hirundo. 
41. Pima. Shell longitudinal, wedge-form, equi- 
valve, pointed and nearly straight at the base, 
dilated and open at top. Hinge without teeth, 
Ligament nearly the length of the shell. 
Includes the whole of this family, 
C. With the Ligament internal. 
42, Ostrea, Shell fixed, inequivalve, irregular, 
with the beaks more or less separated from each 
other and becoming unequal by age. Hinge 
without teeth, with a cavity which is partly 
external and in the lower valve which becomes 
gradually elongated, | 
Includes Ostrea edulis and parasitica. 
43. Anomia, Shell flat, inequivalve, irregular ; 
the under valve perforated near the beak, and 
