MYTILIDAE 357 



with strong, vertical, smooth ribs; remainder of shell smoothish with only 

 irregular growth lines. Commonly found boring into soft coral blocks. 



Lithophaga antillanim Orbigny Giant Date Mussel 



Plate 28k 



Gulf of Mexico and the West Indies. 



2 to 4 inches in length, elongate, cylindrical and colored a light yellow- 

 ish brown on the outside and iridescent cream inside. Sides of valves marked 

 with numerous, irregular, vertical riblets. Fairly common in soft rocks in 

 moderately deep water. 



Subgenus Myoforceps P. Fischer 1886 

 Lithophaga aristata Dillwyn Scissor Date Mussel 



Plate 29) 



Southern Florida and the West Indies. La Jolla, California, to Peru. 



H to I inch in length. Characterized by the pointed tips at the posterior 

 end being crossed like fingers. Color yellowish brown, but generally covered 

 by a smooth, gray, calcareous encrustation. Moderately common in soft 

 rock. 



Subgenus Dibenis Dall 1898 

 Lithophaga bisulcata Orbigny Mahogany Date Mussel 



Plate 28n 



North Carolina, the Gulf of Mexico, and the West Indies. 



I to 1/4 inches in length, elongate, cylindrical and coming to a point 

 at the posterior end. A sharp, oblique, indented line divides each valve into 

 two sections. Anterior half of valve smooth, mahogany-brown, but com- 

 monly encrusted with porous, gray, calcium deposits. Posterior end more 

 heavily encrusted with a gray, porous covering which projects beyond the 

 edge of the shell. A fairly common rock-boring species. 



Lithophaga plujnula kelseyi Hertlein and Strong Kelsey's Date Mussel 



Plate i()i 



San Diego north to Mendocino County, California. 



I to 2 inches in length, similar to L. bisulcata, but the calcareous matter 

 on the posterior end is strongly pitted and furrowed to look like a wet, ruffled 

 feather. Typical plmnula Hanley ranges from Lower California to Peru. 

 Both fairly common in rocks. 



