The Mussels and Rock-eaters 



the posterior area. The dark brown epidermis is tinged with 

 yellow. Ligament long and strong. Lining silvery white. 

 This is one of the most common mussels on the muddy tide flats 

 of our east coast. It has the clinging habits of Mytilus. Length, 

 2 to 4 inches. 



Habitat. — Nova Scotia to Georgia. 



The Tulip Modiola (Af. tulipa. Lam.) is oblong like a small 

 M. plicatula, but striped with alternating rays of yellow and 

 chestnut. It is the gayest of our native mussels, and is naturally 

 a southern species. Length, 2 to 3 inches. 



Habitat. — North CaroHna to West Indies. 



The Straight Horse Mussel (M. recta, Conr.) is long and 

 narrow, with delicate, ventricose shell, shading from dark to 

 lighter brown from the beaks outward, and becoming quite hairy 

 toward the end. Length, 3 to 4 inches. Var. flabella, Gld., 

 grows to greater size. 



Habitat. — Vancouver to southern California. 



Genus MODIOLARIA, Beck 



Shell oblong, with hinge at one end, ribbed radiately, but 

 with a plain central area separating the ribbed portions ; foot 

 strap-shaped, very extensible. This mussel lives in rock crevices, 

 in empty shells, or buried in the tests of simple ascidians. When 

 moved to change its quarters it is active, and uses the tip of its 

 foot as a prehensile organ, grasping stems of seaweed and other 

 objects to help itself along. When a new place is selected, at- 

 tachment is made by spinning a byssus. 



The Black Modiolaria (M. nigra, Gray) changes its outer 

 colour with age from purple or olive brown to black. Its out- 

 line is almost oval, the ribbed areas are crossed by concentric 

 lines so as to form a fine network with knobs at the intersections. 

 Length, 3 inches ; width, 2 inches. 



Habitat. — Arctic seas to Cape Hatteras, Pacific coast, Europe. 



THE ROCK-EATERS 



Genus LITHODOMUS, Cuv. 



Shell thin, cylindrical, inflated in front, wedge-shaped be- 

 hind ; surface finely striated, often wrinkled and furrowed ; 



39' 



