NO. 7 PROTECTIVE ADAPTATIONS McATEE IO7 



" The few species common to the mud flats exposed by the retreat- 

 ing tide are colored black or dark olive." Examples: Ilyanassa 

 obsolcfa, Nassa tr'mittafa. Rissoa ininuta (p. 143). There are 78 

 records of Ilxanassa ohsolcta distributed among 18 species of birds. 

 Thirty-two of these shells were taken at a meal by a greater scaup 

 duck, and from 42 to 62 by each of six knots. There are 98 records 

 of Nassa trkuttaia. two of them beiiig 275 and 285 specimens in the 

 stomachs of greater scau{)s ; and there are three determinations of 

 Rissoa minufa. 



Lacuna v'nicta: The colors " quite match the I.aminarian upon 

 which they are foimd " (p. 143). This species was identified 39 times 

 in nine species of birds in which numbers from 32 to 75 were found, 

 and in one case, that of a golden-eye, no fewer than 116. 



" Margarites licUcina I have found in numbers on the large Lami- 

 narian and on seaweed at low water mark and its color is decidedly 

 protective " (p. 144). Our tabulation shows 10 records of this species 

 of shell, distributed among five kinds of birds. 



"A very evident case of protective coloring is seen in the three 

 species of Crepiihila found on our coast. Crepidula formcafa is drab, 

 variously rayed and mottled with brown, and it lives attached to 

 stones near the roots of the large Laminarian or upon stones clothed 

 with algae of similar colors, or attached to the large Myfilus. Crepi- 

 dula convcxa, a much smaller species, lives on the roots of seaweed. 

 Professor Perkins records its occurrence on the black shell of 

 Ilyanassa ohsoleta. This Crcpidula has a very dark l)rown shell, ac- 

 cording well with the dark color of its various places of lodgement. 

 Crepidida plana or ungiiiforniis lives within the apertures of the shells 

 of larger species of Gasteropods, as Buccimim, Natica. Busycon and 

 others. The shell of this Crepidida is absolutely white " (pp. 144-145). 



All of the limpets named in the foregoing quotation have been 

 identified from the stomachs of nearctic birds, and the total number 

 of records for species of Crepidida is 135. Fifty specimens of 

 C. glaiica were found in one gizzard of a greater scaup duck and 60 in 

 another. The " protection " of C. plana is very undependable since 

 all of the mollusks named as its hosts are swallowed whole by birds 

 and other predatory enemies of shellfish. With reference to a special 

 enemy of limpets " it has been calculated that a single flock of oyster- 

 catchers, frequenting a small Scotch Loch, must consume hundreds 

 of thousands of limpets in the course of a single year." (Cooke. 

 Cambridge Nat. Hist., vol. 3, pp. 56-57, 1895.) 



As an example of the land snails thought to be defended from some 

 enemies by the toothed apertures of their shells, the genus Polygyra 



