1 86 CHIONE. 



The variety ruderata^ Desh., ni-de-ra'-ta, is marked 

 by occasional concentric frills, somewhat like a Rupel- 

 laria ; but it may be distinguished from that shell by 

 the presence of radiating ribs, which its neighbor 

 never possesses. 



Tapes laciiieata^ Cpr. , la-sin-e-a'-ta, resembles sta- 

 minea^ and perhaps is only a southern variety of that 

 species ; but its surface is covered with beautiful net- 

 like sculpturing, quite different from the ordinary 

 form. 



The next shell on our list is Tapes tenerj^inia^ Cpr. , 

 but that species has already been described in the 

 opening chapter on the Lamellibranchs, so I will 

 simply refer you to Fig. 136, and the accompanying 

 description. 



Psephis tantilla, Gould, Se'-fis tan-til'-la. The 

 length of this little shell is only about one-eight of 

 an inch, but it has some quite distinctive marks by 

 which it may be identified. Its shape is somewhat 

 triangular, its surface very smooth and bright, its 

 color white or brownish, with an internal purple 

 spot near one end. It reaches Puget sound on the 

 north, and is probably found along the whole western 

 coast of the United States. 



Chione simillima^ Sby., Ki-o^-ne si-mil'-li-ma, is a 

 species found on the southern coast. The valves of 

 the shell are very thick and strong, and are finely 

 sculptured in both directions. The radial lines are 

 rounded, while the concentric ones are sharp and 

 thin. At the end of the shell is a conspicuous cor- 

 date lunule; on the top is a broad depression, and at 

 the base of this is the external ligament. The car- 

 dinal hinge-teeth are three in number, the pallial line 

 almost entire, showing that it is not a deep burrower. 



