MYTILIDAE 351 



Crenella columbiana Dall British Columbia Crenella 



Figure 26g, h 



Aleutian Islands to San Diego. 



A little over H inch in length, oval-oblong, inflated, with numerous very 

 fine, decussate radial ribs. Color greenish yellow-brown. lo to loo fathoms. 



Genus Modiolus Lamarck 1799 



This group of mussels have shells of various forms in which the hinge is 

 without teeth. The anterior end of the shell extends in front of the beaks, 

 while in Mytilus 3 to 5 tiny teeth are present on the hinge and the beaks are 

 at the very anterior end of the shell. Volsella Scopoli has been rejected. 



Modiolus modiolus Linne Northern Horse Mussel 



Figure 26) 



Arctic Seas to northeast Florida. Arctic Seas to San Pedro, California. 



2 to 6 inches in length, heavy, with a coarse, rather thick, black-brown 

 periostracum which in dried specimens flakes off to reveal a mauve-white, 

 chalky shell. One of the largest and commonest mussels found in cooler 

 waters below low-water mark. Do not confuse with M. americanus. 



Modiolus ajnericajms Leach Tulip Mussel 



Plate 35I 

 North Carolina to the West Indies. 



1 to 4 inches in length, smooth, except for the periostracum, which is 

 commonly hairy and sometimes resembles a beard. Color light-brown flushed 

 with deep rose and sometimes with several radial streaks of light-purple. An- 

 terior ventral area with a deep chestnut splotch. Interior dull white, some- 

 times stained with bluish, rose or brownish. 



Recently killed specimens are commonly washed ashore in large num- 

 bers. A very common species. Formerly known as Volsella or Modiolus 

 tulipa Linne or Lamarck. The subspecies found in Charleston Bay, North 

 Carolina, and Tampa, Florida, is more compressed and a soft brown in color. 



Modiolus demissus Dillwyn Atlantic Ribbed Mussel 



Plate 28h 



Gulf of St. Lawrence to South Carolina. Introduced to California. 



2 to 4 inches in length, black-brown in color, often shiny, and with 

 strong, rough, radial, bifurcating ribs. Interior bluish white with the poste- 

 rior end flushed with purple or purplish red. This is the only ribbed Modi- 

 olus in our waters, but do not confuse it with Brachidontes recurvus which 



