108 ANALYTICAL INDEX. 



CHAPTER III. continued. 



MYTILCS POLYMORPHUS (Dreissena polymorphaj, . PACK 66 



Considered of foreign origin, .... ib. 



Description of the species, . . . . ib. 



Inactive dwells in fresh water, .... ib. 



2. MODIOLA 



Mytilacean tribe dismembered by modern authors, . . ib. 



MYTILUS MODIOLUS Linn. (Modiola modiolusj The Horse Mussel, ib. 



Largest of the race of mussels, .... ib. 



Description of the animal, . . . . ib. 



Often overspread with corallines, .... 67 



MODIOLA BARBATA The Bearded Mussel, . . . ib. 

 Smaller than the former, and considered by some a distinct species, ib. 



Resembles the Modiola in everything. . . . .68 



MODIOLA DISCREPANS The Corded or Corduroy Mussel, . ib. 



Doubtful whether this subject should be thus classed, . . ib. 



Shell a rude oval, eighteen lines by nine, ... ib. 

 Surface striated, ...... ib. 



Species comparatively rare, ..... ib. 



Plate XII. described, . . . . 65-68 



3. ANODON AVONENSIS (A. cygneusj, . . . . ib. 



Shell and animal described, ..... ib. 



Plentiful in Lochend, . . . . . .69 



Plate XIII. described, ..... ib. 



4. CYCLEAS CORNEA, ... ib. 

 Shell globular, three-eighths of an inch in diameter, . . ib. 

 Description of animal, supposed of ascidian nature, . . ib. 

 Motions of the species, . . . . . . ib. 



Spawn in September, . . ... ib. 



Plentiful in Lochend, ...... 70 



5. TKI.LINA, ....... ib. 



Shell and animal described, . ' '. . . . ib. 



Motions vehement, ...... ib. 



6. VENCS VIRGINEA (Tapes pullastraj , ' . . . .71 

 Shell and animal described, ..... ib. 



