86 A. M Yeri'ill — Study of the family PectinidcB. 



and straight; aui'icles relatively large and broad, both ends sub- 

 truncated or a little convex in the left valve, and forming nearly a 

 right angle with the dorsal margin ; anteriorly not well differentiated 

 from the body of the shell. In the right valve the anterior auricle is 

 narrow and somewhat more elongated and obtusely rounded at the 

 end, with a sharp, angular, byssal notch beneath it and separated 

 from the body of the shell by a narrow groove. 



The dorsal margins of the body of the shell are nearly straight and 

 form rather more than a right angle. Ventral margin broadly 

 rounded, nearly serai-circular, forming a very obtusely rounded 

 angle where it joins the dorsal margins. Umbos a little prominent, 

 with a small, smooth, rather acute, incurved beak, which usually 

 projects a little above the hinge-margin. 



The surface of the left valve is everywhere thickly covered with 

 fine, almost microscopic, radiating striae, which become a little more 

 distinct on the anterior auricle ; on some parts of the shell very thin, 

 slightly raised, concentric lamellae or lines of growth are often dis- 

 tinct, especially on the anterior auricle, where they become closer 

 and more regular ; in crossing the radial striations they produce a 

 microscopic decussation, which is often quite regular. The sculpture 

 on the posterior auricle, though finer, is similar, but in many speci- 

 mens the surface is nearly smooth or marked only by very fine radial 

 striae. The body of the shell of the right valve is smooth, except 

 for very fine concentric lines; on the anterior auricle are three to six 

 or more distinct radial ridges, which are roughened by conspicuous 

 lines of growth ; the margin below the byssal notch is entire ; the 

 posterior auricle is nearly smooth. 



The internal hinge-plate is thin in the middle, but relatively broad 

 on each auricle, and is crossed by numerous fine, well marked, trans- 

 verse incisions ; these are much more conspicuous than in most of 

 the related species, whether young or old. The resilial pit is small, 

 rounded, and situated just under the beak. There are no internal 

 lirsB. The inner surface is smooth and glossy, although in fresh 

 specimens the external radiating lines show through by translucency. 



The ground-color of the right valve is yellowish or grayish white, 

 with more or less numerous light yellowish brown, or reddish brown 

 spots and blotches, and sometimes with irregular patches of opaque 

 white ; right valve white, sometimes with a few yellowish-brown 

 spots. Some specimens are nearly destitute of spots. 



The right valve is less convex than the left, and its ventral edge 

 does not quite reach that of the opposite valve ; the umbo is less 



