PELECYPODS 



423 



Yulilia sapotilla. 



two and a half inches in length and one and a half inches in height, 

 and is dark olive-green. The foot is like that of Y. limatula. The 

 labial palps are exceedingly large. 



Y. sapotilla. The shell is 

 ovate, prolonged on one side, 

 thin, fragile, translucent, and 

 covered with a thin, glossy epi- 

 dermis, greenish in color. The 

 anterior half is semi-oval, the 

 posterior portion narrowed and 

 compressed ; within it is pearly- 

 white, with a triangular cartilage 

 cavity, and 

 sixteen to eigh- 

 teen pointed 

 teeth on each 

 side. In length 



it is little less than an inch. Found from Long Island 

 Sound northward. 



FAMILY SOLENOMYID.E 

 GENUS Solenomya 



Two species of this genus, which are greatly prized by collectors 

 on account of the extraordinary development of the epidermis of 

 the shell, occur in New England waters. The strong corneous 

 periostracum of a deep chestnut-color projects considerably be- 

 yond the margins of the valves ; the shells are exceedingly thin 

 and fragile, and are marked with radiating 

 lines. The two species are easily distinguished 

 by their difference in size. S. velum is about 

 one inch long and one half of an inch high. 

 S. borealis, of arctic range, is quite twice that 

 size. Their anatomy is similar in essentials to that of Yoldia. 

 These species live near shore in sandy bottoms, and are occa- 

 sionally found upon the beach between tides. Chelsea Beach, 

 just north of Boston, is an often-quoted locality. 



ORDER FILIBRANCHIATA 



There are several families of this order which are well repre- 

 sented in both the Atlantic and the Pacific waters of the United 

 States. The characteristic feature of this group of bivalves is the 

 filamentous gill, that is, a gill with the filaments long, doubled 

 back, and united to each other only by ciliary junctures. These 



Solenomya velum. 



