




























SHELL DREDGING. 271 
s 
under the magnifier. Then there are certain- species of 
shells (Chiton, Pl. 4, fig. 1) which cling to the stones, limpet- 
like, but instead of having a shell of one piece covering 
their back, the shell is composed of eight transverse pieces, 
one lapping over the other. When detached from the rock 
they often roll up like a pill-bug. On the eastern coast of 
Maine there is one large species which can be taken from 
the rocks at low-water mark. The species dredged in Mas- 
sachusetts Bay are generally small; one or two of them are 
brightly colored with shades of red. s 
Two other species called Velutina (PI. 4, figs. 4, 5) are 
often found adhering to the rocks brought up in this man- 
ner. By far the most beautiful and interesting animals are 
contained in the little cells which often cover the rocks from 
deep water. They are arranged in little patches like mats, 
some species making a perfectly circular figure, others cov- 
ering the rocks in irregular patches. These belong to the 
lowest group of mollusks, and are called Polyzoa. Under 
the microscope the mass is seen composed of little cells, 
arranged like the stones in a pavement. Each one of these 
cells has a little opening protected by a small lid, which 
opens to allow the animal within to protrude a tuft of minute 
feelers. It would require too long a time to show the affin- 
ity of these animals to the clam and oyster, yet they are 
among the lowest forms of this group. There are many 
Species on our coast, some of which have been described as 
hew, others are similar to British species. 
We figure on Plate 4 several species of shells one is likely 
to dredge on our New England coast, though representing 
but a small portion of the species that may be found, 
‘nd we may mention here, with propriety, that the State 
of Massachusetts—with that liberality that has always char- 
acterized the acts of its legislature—has now in preparation 
.* new edition of *Gould's Report on the Invertebrate ani- 
mals of the State," This book, when published, will contain - 
. “arefully engraved figures of all the species of shells found 
