PECTEN. 291 



specimens, that we ventured to decide upon uniting it with 

 the more typical form. It is ahnost invariably smaller, 

 with its surface wholly or partially sculptured with radi- 

 ating striae ; its ribs, which are more frequently five than 

 six in number, strongly, and rather abruptly elevated, 

 and its hinder auricle very decidedly the smaller one. In 

 some of the younger individuals, the very delicate wavy 

 concentric elevated wrinkles Avhich cross the striae, give a 

 slightly squamular or at times a subcancellated appearance 

 to the shell. The white speckles are not so diffused as in 

 the previous form, but are generally visible on one, at least, 

 of the umbones. In the very beautiful example figured 

 (belonging to Mr. Barlee, whose indefatigable exertions in 

 collecting, have rendered many of our once scarcer sj)ecies 

 comparatively common), some of the interstitial striae are 

 crested with small spinous scales. 



Intermediate between the two, comes a third variation, 

 which more closely approaches the former, but differs in 

 being stronger, more equilateral, and more frequently 

 striated ; its ribs are more prominently defined (and in the 

 young are subangular) ; its dorsal slopes more rectilinear ; 

 its hinder auricle, likewise, is rather smaller in proportion, 

 more incurved laterally, and with its sinus (in the young) 

 more angulated and better indicated. 



A moderately sized specimen of the typical form 

 measured, an inch and five lines in length, and an inch and 

 six lines and a-half in breadth : its hinge-margin was equal 

 to exactly one-half the length of the shell. The dimensions 

 of the largest individual noticed by us, of the second variety, 

 were an inch and three lines for the length, and one line 

 more for the breadth ; the hinge-margin measured under 

 seven lines, thus causing the auricles to be shorter in pro- 

 portion to the general area. 



