[413] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 119 



distinguish with certainty the animals properly inhabiting the gravelly 

 and shelly bottoms from those that pertain to the muddy and sandy 

 bottoms, but for our present purposes it is not necessary to make a very 

 sharp distinction between the different lists, for many species arc com- 

 mon to all, and the areas of the different kinds of bottom are generally 

 small in this region, and evidently may change their character from 

 time to time. 



After a single storm the character of the bottom, in some localities, 

 was found to be greatly altered over wide areas, sometimes several miles 

 in extent, at depths of two to ten fathoms, and the animal life at the bot- 

 tom was always found to have changed very quickly, when the physical 

 character of the bottom had been modified. The most frequent cause 

 of change was the accumulation of immense quantities of dead sea- 

 weeds and eel-grass over bottoms that, a few days before, had been per- 

 fectly free from it. Such accumulations must either kill the majority of 

 the animals inhabiting gravelly, sandy, or rocky bottoms, or else cause 

 them to migrate. In all probability the majority of them perish, at 

 such times, beneath the accumulations. In other cases one or two 

 storms sufficed to change gravelly and shelly bottoms to sandy ones, 

 causing, undoubtedly, great destruction of life and a great change in its 

 character over particular areas. These changes in the character of the 

 deposits accumulating on the bottom, attended with extermination of 

 life and changes in its character in particular localities, illustrate on a 

 small scale similar phenomena that have constantly occurred on a 

 grander scale in the history of the past life of the globe, during all the 

 geological ages, from the first commencement of life. Practically it was 

 found quite difficult to find, in this region, large areas of gravelly and 

 shelly bottoms, without some admixture with mud or sand, and it very 

 seldom happened that a continuous series of dredgings could be 

 made on such bottoms without encountering patches of mud and sand. 

 Therefore the accompanying list of species undoubtedly contains many 

 that belong rather to muddy or sandy bottoms than to those now 

 under discussion, for species have not been excluded unless well known ? 

 from many observations, to be peculiar, or nearly so, to mud or sand 

 and rarely met with on true hard bottoms. 



The following are the principal localities where this kind of bottom 

 was explored in Vineyard Sound and vicinity, but those belonging to 

 the outside cold area are not included : 



First. An extensive area extending from off* Nobska Point eastward, 

 nearly parallel with the shore, with some interruptions of sandy bot- 

 tom, as far as Suconesset Shoal, mostly in three to eight fathoms of 

 water; on this bottom were the dredgings of line 6, a, 6, c, rf, e,f; 21, 

 a, &, c, d; 22, , 6, c, d; 23, , &, e,f; 25, 6, c, d; 26, a, 6, c, rf, e; 34, 

 a, &, c, d, e,f; 35, a, fr, c, <7, e. 



Second. Another similar region nearly parallel with the southeastern 

 shores of Naushon and Nonamesset Island and extending out into mid 



