38 WEST COAST SHELLS 



the Pea-pod Shell. Among the difficult things to 

 explain is the fact that a mollusk with a thin and 

 flexible shell can bore a deep hole into hard rock. 

 But this creature does it, for I found the rocks of 

 Duxbury Reef at Bolinas almost alive with this and 

 other borers. It spins a byssus, too, like other mus- 

 sels, and attaches itself to the sides of its burrow, 

 though this would seem to be an unnecessary bit of 

 precaution, inherited from the time when its ances- 

 tors lived in more exposed situations. The figure 

 represents a rather large specimen. The inside of the 

 shell is white and pearly, while the outside is covered 

 with a dark chestnut epidermis, which has numerous 

 transverse wrinkles. 



Adula stylina^ Cpr., the Short Adula, is smaller, 

 shorter, and has very angular shells, with a brown 

 epidermis destitute of distinct wrinkles. 



Lithophagus plumula, Hani., the Rock-eating 

 Mussel, has a small, cylindrical shell, rounded in front 

 and tapering behind. It constructs a burrow sometimes 

 in rocks and sometimes in old shells. It has a light 

 brown epidermis, and is an inch or two in length. 



Modiolaria taylori^ Dall, Taylor's Modiolaria, is 

 a little creature hardly a quarter of an inch long, but 

 shaped like a true Modiolus. It was found in tide- 

 pools, at Victoria, B. C, by Rev. G. W. Taylor. 



Modiolaria vernicosa, Midd., the Varnished Mo- 

 diolaria, has an oval shell, with beaks near one en8: 

 It is smooth, reddish-brown, and has a brilliantly 

 polished epidermis. Its length is 15 mm. It is found 

 in Alaska, where there are other species of the same 

 genus, which we will not now describe. 



