SHELLS OF SOUTH AMERICA. 49 
418. CrREPIDULA DILATATA, Lamk., d’Orb. Voy. v. 465. 
£, 58.. 4: 6. B.M. 
Crepidula Peruviana, C. depressa et C. patula, Desh. 
Crepidula Adolphei et C. nautiloides, Lesson. 
Crepidula dilatata, C. pallida, C. strigata, et C. ungui- 
formis, Brod. 
S. America. 
C. Patagonica, C. arcuata and C. protea are only varieties of 
C. dilatata, caused by the form of the substance to which they 
are attached. They are often parasitic on each other. It may 
be doubtful if the Patagonian specimens of C. aculeata are not 
also varieties of this species, and distinct from those found in 
Rio de Janeiro, C. foliacea being apparently intermediate between 
C. dilatata and the specimen of C. aculeata from Peru. Indeed 
the species of these Mollusca require other characters to distin- 
guish them, besides the general form of the shell and the structure 
of its surface: each species presents the same variety, according 
to the locality and form of the surface to which it has been at- 
tached; and these forms from different localities have been con- 
sidered the same species, instead of varieties of some peculiar 
local species ; hence C. fornicata, C.aculeata and C.unguis have 
been said to be found in many parts of the world, which is in- 
consistent with our knowledge as regards other Mollusca, but 
may be the case with these, as they sometimes attach themselves 
to ships, floating wood, &c., and may be thus carried from one 
part of the world to the other, and hence obtain a larger geogra- 
phic distribution than other Mollusca. 
The outline of the front edge of the imner lip appears to be 
changed, as well as the outer form of the shell, by the form of 
the substance to which the animal is attached; thus m the un- 
guiform varieties of C. dilatata the front edge of the inner lip 
“is straight, while in most other varieties it is produced, rounded, 
with a deep sinus on the left side. 
419. CREPIDULA FOLIACEA, Brod., d’Orb. Voy. v. 468. B.M. 
Bolivia. 
420. CREPIDULA ARCUATA, Brod., d’Orb. Voy. v. 468. B.M. 
Peru; Payta. 
421. CREPIDULA INCURVA, Brod., d’Orb. Voy.v. 468. 
Peru; Payta. 
D 
