Morse.] 152 [April 5, 



statements of Forbes and Hanley, and expresses his belief in their 

 correctness, and in describing some peculiar features of asymmetry, 

 aptly calls them the Pleuronectes among mollusks. 



In examining some dried sea weed collected by a friend of mine 

 during the last week in March, I noticed some very young Anomise 

 clinging to it. Unfortunately nothing but the little dried shells were 

 left for examination, but as these presented some exceedingly inter- 

 esting points as bearing upon the homology of the plug to the byssus, 

 I may be excused for presenting such incomplete observations. The 

 specimens were easily detached from the sea weed with the point of 

 a knife, without fracturing the shells; they were consequently very 

 lightly attached. The smallest specimens examined are quite orbicu- 

 lar, the upper, or left valve, is very tumid near the nucleus, the 

 lower or right valve is flat and somewhat smaller than the upper 

 valve. The foramen, or sinus, is not closed, but opens on the anterior 

 border of the shell. The chief point of interest, however, is seen in 

 the nucleus, or that portion of the shell first formed when the animal 

 was free and roving. This early condition of the shell is distinctly 

 marked at the beak in both valves. It is yellowish in color, and marked 

 with numerous, very regular concentric lines of growth, while the re- 

 maining portion of the shell is colorless or white with irregular lines of 

 increment. The nucleus is oblong-oval. The umbones are nearly 

 central though nearer the anterior margin, and the shell is more 

 globose behind. Both valves of the nucleus appear equally convex, 

 and no sign of a sinus or perforation is visible in either valve. On 

 the free edge of the right valve, directly under the umbo, a dis- 

 tinct notch is seen, the lines of growth indicating it, and showing that 

 the edge of the shell is not absorbed to form this notch. It will be 

 noticed that this marginal notch appears in that valve which is 

 below, and which afterwards presents the opening for the passage of 

 the byssal plug. 



The condition of the shell at this time clearly indicates that the 

 animal is not only already attached, but has fallen to one side, and 

 while in this position has added a few more lines of increment to its 

 larval shell, as no sign of this notch is seen on the left or free valve. 

 Soon, however, the peculiar and rapid secretion of a different shell 

 growth takes place; the lines of increment are no longer regular, nor 

 so conspicuous, and the shelly matter is white. The left valve adds 

 concentric layers around its entire margin, not excepting the hinge 

 margin. The lower valve appears to grow from its posterior and 



