BUCCINUM. 181 



A glance at the condition of things at once revealed the 

 mystery of these dwarfed males. The ledge on which these 

 specimens were found is partly exposed at low tide, and is at all 

 times washed by impetuous currents, so that it is quite difficult 

 to land. 



A study of the surface features of the ledge indicated the force 

 of the tidal currents. There were no loose fragments, of rock 

 upon it, save those which were so tightly wedged in the crevices 

 of the ledge that they could not be worked out with the hands. 

 The specimens of Buccinum in every case were found hid away 

 in nooks, and concealed in the cracks and crevices marking the 

 ledge. It was clearly obvious that only the smallest males could 

 work their way into such constricted quarters for the purpose of 

 uniting with the females, and that the smaller males had the ad- 

 vantage over the larger males in this respect, there could be no 

 question. The true state of the case was so instantly seen, that 

 though hundreds of specimens were collected with the object of 

 determining whether in any case a large male occurred, not a 

 single exception was met with in which the female was not being 

 fertilized by a diminutive male. 



The constrained position in which these were found precluded 

 the possibility of a large male with his cumbrous shell getting 

 close enough to the female in her narrow quarters to perform the 

 sexual act. The smaller males having this advantage, have from 

 generation to generation perpetuated their dwarf characters. It 

 would seem from these facts that natural selection has worked 

 in an unusual way in producing secondary sexual characters, 

 rarely, if ever, seen in gasteropods. 



Both males and females presented a wide range of variation in 

 the characters of the shell, some of them showing very distinctly 

 the oblique folds so characteristic of the species, while in others 

 these folds were scarcely visible. The shell of the male is 

 smoother than that of the female, and is also more slender and 

 more delicate. The figures represent normal males and females 

 from this peculiar colony.* 



Gould supposed that BUG. undatum did not occur south of 

 Cape Cod, Massachusetts, a point believed in his da}^ to separate 



Proc. Bost. Soc. Nat. Hist., XVIII, 284, 1876. 



