— 39 — 



shell is marked with bold radiating ribs recalling the true cockle 

 {Cardium) though the shell is distinctly longer in proportion to its 

 height. The foot is flattened and though strong is not as large as 

 the finger-like foot of the cockle. It differs from P. ienerrima in 

 showing comparatively faint growth lines and in having the inner 

 margins of the valves roughened and not smooth. 



Habitat and habits — It is not adapted by its form or burrowing 

 powers to loose or rapidly shifting ground such as that occupied by 

 the razor clam, but is still active enough to maintain itself on outer 

 beaches as well as in enclosed waters. In the ba.ys it is found in much 

 the same situations as is the AVashington clam (Saxklomus), never in 

 beds of deep soft mud, but nearer the entrances of the bays and as a 

 ride not far distant from low tide line. In firm mud banks it burrows 

 to a depth of from three to eight inches though occasionally it is 

 found at the surface. It does not inhabit pure sand through which 

 its rough shape unfits it to move rapidly, but it is often met with 

 wherever there is room for it to nestle in accumulated gravel and 

 sand among the rocks in exposed situations. Along the outer coast it 

 is therefore possible to .judge fairly accurately of its distribution by 

 the presence of firm beaches, such as those of small boulders mixed 

 with gravel or coarse sand. It is capable of living in gravel or 

 boulder beaches below low tide line ; from such beaches live clams are 

 frequently washed ashore, as is the case on the pure sand beaches off 

 the Humboldt Bay spits and off Crescent Beach. Naturally, however, 

 clams in such situations are only indirectly of commercial value through 

 forming a source of supply of spawn for the neighboring exposed 

 beaches. 



Distribution and use — The following localities in Northern Cali- 

 fornia contain beds large and well stocked enough to warrant more 

 than casual digging. All were carefully inspected during good tides 

 (W. F. T., 1910) except those in brackets, where the ground seemed 

 favorable and local information repoi'ted the presence of the rock 

 cockle. 



Tnilrieh.s Runcli, near the Oregon Line. 



Point St. George to Crescent City. 



Nicl^el Creek (below Crescent City). 



Damnation Creelv, and between Damnation Creek and Wilsons Creek. 



False Klamath Cove. 



Patricks Point.. 



Trinidad, between one-half to one and one-fourth miles east. 



Humboldt Bay. 



Cape Fortunas. 



Mussel Ranch (Cape Mendocino). 



Morgans Point. 



Shelter Cove, inside Point Delgada. 



Abalone Point, near Westport. 



Fort Bragg. 



Bridgeport Landing, near Point Arena. 



Irish Gulch. 



Arena Cove. 



[Iversons Landing]. 



[Haven's Neck]. 



Bowen's Landing. 



Gualalla (or Walalla) Point, and Del Mar, two and one-half miles south. 



[Russian River, both sides a mile distant, a few]. 



