120 BULLETIN OF THE BUREAU OF FISHERIES. 



It is to be noted that this preponderance in favor of the Buzzards Bay stations 

 relates only to those of the Fish Hawk. It is in the deeper portions of the Bay, where 

 the Fish Hawk dredgings were made, that the mud predominates. Elsewhere the bot- 

 tom agrees more closely with that of Vineyard Sound. 



These same facts are shown by a comparison of the lists of "prevalent' ' species for the 

 different groups of stations (p. 65-71)4. e., the lists of those species which were taken at 

 one-fourth or more of the stations belonging to each group. Thus the list for the Fish 

 Hawk stations of Vineyard Sound contains five species ; that for the Fish Hawk stations 

 of Buzzards Bay, nine species. The list for the Phalarope stations in Vineyard Sound 

 contains five species; that for the Phalarope stations of Buzzards Bay, six species. 



With reference to the wealth of annelid life upon the three types of bottom which 

 we have considered, we have the following figures, representing the average number of 

 species per dredge haul: Sand, 3.4; stones and gravel, 4.7; mud, 5.2. 



To what extent the greater wealth of annelid life upon muddy bottoms is actual 

 and to what extent it is apparent can not be stated. Soft mud is of course cut into 

 much more deeply with the dredge than is sand or gravel, and thus a larger proportion 

 of the burrowing worms would be collected from the former type of bottom, even if they 

 were equally common upon both. 



Those species which were taken in one-fourth or more of the dredge hauls made upon 

 sandy bottoms are : ° 



Harmothoe imbricate. Hydroides dianthus. 



Nereis pelagica. Lepidonotus squamatus. 



Diopatra cuprea. 



It will be seen that this list comprises exactly the same species as were recorded 

 for one-fourth or more of the total number of stations. It likewise comprises the same 

 species as are to be found in the lists for both the Fish Hawk and Phalarope stations in 

 Vineyard Sound. 



The following is a list of prevalent species (according to the same standard) taken 

 upon bottoms of gravel and stones : 



Hydroides dianthus. Harmothoe imbricate. 



Nereis pelagica. Diopatra cuprea. 



Lepidonotus squamatus. Pseudopotemilla oculifera. 



The only one of these which was not comprised in the preceding list is the last one 

 named. 



The corresponding list for muddy bottoms is as follows : 



Hydroides dianthus. Harmothoe imbricate. 



Diopatra cuprea. Ninoe nigripes. 



Nephthys incisa. Cistenides gouldii. 

 Clymenella torquata. 



Three of the foregoing species (Hydroides, Diopatra, and Harmothoe) were comprised 

 in all of the preceding lists, and indeed they may be regarded as almost ubiquitous in 

 local waters. The other four are to be regarded as characteristic of muddy bottoms, 

 and indeed all of the seven appear among the "prevalent" species for the Fish Hawk 



a In this and all similar lists, the species are arranged in the order of frequency. 



