1871.] 145 [Bicknell. 



species of Gasteropods, as Buccinum, Natica, Busycon and others. 

 The shell of this Crepidula is absolutely white. 



There are many species that undoubtedly receive protection in al- 

 lowing foreign substances to grow upon their shells, and these species, 

 oftentimes covered by a dense growth of calcareous or other algEe, 

 are difficult of detection by the experienced collector. 



There are also certain species that habitually accumulate foreign 

 substances upon their shells. The little Pisidium ferrugineum possibly 

 finds greater immunity from danger in its habit of accumulating a fer- 

 rugineous deposit on that portion of the shell most conspicuous. Nu- 

 cula delphinodonta has likewise a similar habit. The delicate Lyon- 

 sla arenosa, with its habit of entangling particles of sand in its epi- 

 dermal filaments, undoubtedly finds protection in this peculiarity. 



It was not the intention to go outside of New England species in 

 citing these examples, but in this connection I cannot forbear men- 

 tioning the tropical genus Phorus. The species are said to frequent 

 rough bottoms and to scramble over the ground like the Strombs and 

 not to glide evenly. This peculiar manner of moving would render 

 them very conspicuous, and it is curious to observe that most of the 

 species attach foreign substances to the margins of their shells as they 

 grow, so that when a shell has attained its growth it is almost com- 

 pletely concealed by fragments of shells large and small, spines of 

 Echini, bits of coral and stones. 



These feAV observations are offered (and they might be multiplied) 

 with the belief that if there is any truth in the theory of protective 

 coloring as advanced by Wallace, the various colors of Mollusca in 

 many cases can be explained, and the occurrence of varieties in color 

 are also accounted for by the same theory. 



Mr. Edwin Bicknell remarked that animals in preying 

 upon each other were attracted more by the sense of smelL 

 than that of sight. He had noticed on one occasion, when, 

 jelly fishes were stranded, that numerous carnivorous snails, 

 Lacuna vincta, were seen moving from all points towards 

 them. He thought they could be directed only by a acute 

 sense of smell. 



Dr. B. Joy Jeffries called attention to the probability that 

 the animals which prey upon those supposed to be pro- 

 tected by want of color, or by being of the color of their 



PROCEEDINGS B. S. N. H. — VOL. XIV. 10 DECEMBER, 1871. 



