33 



The shell, about tliree inches hiji^h, is e(iuilateral, and lias 

 cl^ep erenations extendinfi: from the apex to the margin. The 

 valves are etiuai in size, the lower (right) sliglitly more arched 

 tl:an tlie upper. The hinge margin is broad, nearly straight, 

 with e(pial eai-s. A sliallow byssal notch at the bfuse of the an- 

 terior ear on tho right valve is deeper and more pronounced in 

 the young specimens than in the adult. The shell varies in color 

 from pale straw to reddish orange or dark brown. The ui)per 

 valve is usually covered with a mat of fine algae, silt and worm 

 tubes, which aid nuiterially in concealing the scallop as it lies 

 on the bottom among the blades of eel grass. 



The following description of the scallop l)y Dr. Sterns is 

 given by Dr. Smith in the report already referred to: "The 

 enamel of the fan shell is exceedingly beautiful. The mantle, or 

 thin outer edge, which is the part nearest the rim or edges of 

 the valves, conforms to the internal structure of the latter, and 

 presents the appearance of a delicately pointed ruffle or frill. 

 This mantle is a thin and almost transparent membrane, 

 adorned with a delicate fringe of slender thread-like processes 

 or filaments, and furnished with glands which secrete a coloring 

 matter of the same tint as the shell. The valves increase in size 

 ill harmony with the growth of the soft parts by the deposition 

 around and upon the edges of membranous matter from the 

 fringed edge of the mantle which secretes it. This cover is 

 also adorned with a row of conspicuous round black eyes around 

 its ba.se. The lungs or gills are between the tw^o folds of the 

 mantle, composed of fibers pointing outward, of delicate form 

 and free at their outer edges so as to float loosely in tbe water. 

 • The mouth is placed between the two innermost gills, where 

 they unite. It is a simple orifice, destitute of teeth, but with 

 four membranous lips on each side of the aperture. The mechan- 

 ism by which respiration and nutrition are secured is elaborate 

 and exceedingly interesting. The filaments of the gill fringe, 

 when examined under a powerful microscope, are seen to be 

 covered with numberless minute hair-like processes, endowed 

 with the power of rapid motion. These are called cilia, and 

 when the animal is alive and in .^ilii, with the valves gaping, 

 may be seen in constant vibration in the water, generating by 



