308 TRANSACTIONS OF THE [aPR. 12, 



It is of great interest to watcli Zirphsea feeding. As the 

 large numbers of diatoms and otLier small organisms are floated 

 about by the receding or more especially by the encroaching 

 waves, they are caught in a little vortex of water which may be 

 seen pouring in at the inhalent opening, the margin of which, 

 with its large papilloe, is extended funnel shaped. One can not 

 doubt that this is dinner time for the prisoner below. 



Pholadidea is found associated with Zirphsea, but here in the 

 clay it does not seem to get along in life so well. It prefers the 

 shales and sandstones of the open coast where the breakers dash. 

 The largest specimens found in the clay were quite small 

 (2-5 cm.) as comi^ared with those found in other and more pre- 

 ferred habitats. 



The closely allied genus Parapholas is also found on Puget 

 Sound. The writer is indebted to Professor I. C. Russell of the 

 United States Geological Survey for a specimen of the shell 

 found in soft sandstone at Pt. Blakely and to Mr. Trevor Kincaid 

 of the University of Washington for a complete specimen of the 

 same. Here it lives in the rock and is vei'y much like Pholadidea 

 in its habit. The structural differences will be referred to later. 



Teredo (sp. und.) is abundant in the pilings of wharfs, and in 

 driftwood, 



Adula falcata may be found associated with the above men- 

 tioned forms (excepting Teredo) and attached to the sides of 

 burrows near their mouths by means of a byssus. This form is 

 related rather to the mussels than the clams. 



In Zirphsea the two valves of the shell articulate on the umbo, 

 and there is thus formed a double ball joint about which the 

 valves are free to move mutually in any plane. Anteriorly the 

 shell gapes above (the antero-dorsal opening) and below (the 

 antero-ventral opening). Through the antero-dorsal opening 

 protrudes a thickened lobe of the mantle, and below through the 

 antero-ventral opening is thrust the foot. 



The valves meet about midway their ventral length, and gape 

 again posteriorly for the accommodation of the monstrous 

 siphon. Externally each valve may be seen to be divided b}^ an 

 oblique line running downwards and backwards from the umbo 

 into two areas, a forward triangular area marked obliquely with 

 the prominent ridges of successive shell accretions and a pos- 

 terior smoother area. A greenish " epidermis " is present but is 

 only fragmentar}', because of wear and tear. 



Externally about the umbo is a roughish nacreous patch de- 

 posited by the antero-dorsal mantle lobe and serves for the at- 

 tachment of the anterior adductor muscle, which is found at this 

 point imbedded in the antero-dorsal mantle-lobe. 



