zoology: marine invertebrates. 71 



coarser surface, thick coarse epidermis of a dusky brown color, 

 and less convexity of valves. 



Another large and handsome shell, found occasionally on Re- 

 vere beach, is Thracia conradi, distinguished by its peculiarly con- 

 stricted posterior end, toothless hinge, and disparity in size and 

 convexity of the two valves. It is found only after violent north- 

 east storms, but probably lives buried in the sand a little below low 

 water (Gould) . Zirphcea crispata also is found occasionally after 

 storms. This is one of the most striking shells of our shore, dis- 

 tinguished by the highly ornamented anterior and smooth posterior 

 portion of each valve. 



The most abundant shell on this beach after a northeasterly storm 

 is the razor shell, Ensatella americana. The animal lives in the 

 sand and mud above and below low water, and may be obtained 

 alive by digging at low tide. The shells may be found by the 

 thousand in spring, or after autumn storms, on the beach near 

 Oak island station, where they are present in all sizes. Associated 

 with this species usually occurs Siliqua costata, although this is 

 commonly less abundant. It looks somewhat like a short Ensa- 

 tella, and is recognized by the color of its epidermis, which is 

 yellowish green blended with livid violaceous (Gould) ; and by 

 the two whitish rays, one passing backward, the other nearly 

 straight downward. The strong rib on the interior of the valve 

 is also a distinctive mark. 



One of the most beautiful species found on this beach is the 

 little Solemya velum, the epidermis of which projects beyond the 

 ed^e of the shell like a curtain, with a scalloped margin. It is 

 especially abundant early in the year, and is to be sought among 

 the seaweed and shells near the water's edge at low tide. The 

 larger and less convex S. borealis is occasionally also found on this 

 beach and is distinguished by its size and grayish blue or lead 

 color. 



Another beautiful shell, occasionally abundant, is Lyonsia hya- 

 lina, readily recognized by its delicate pearly and translucent char- 

 acter and radiating surface strise. It is to be sought at low water 

 in the sand and among seaweeds. Binney and Gould state that 

 "in April, 1836, the beach at Chelsea [Revere beach], was strewn 

 with multitudes of very large and mature " shells. 



The shells of the common mussel, Mytilus edulis, and the horse- 

 mussel, Modiola modiolus, are common upon this beach ; the former 



