90 
JVatural Ilistorij Society of JV. 7?., Bulletin No. IV. 
Tn great abundance on muddy bottoms below low water mark dwells 
tlie longitudinally ribbed, nearly circidar Astarte sulcata. The 
larger and darker colored smoother Cyprina Islandica is less abun- 
dant but in similar situations, as is also the strongly radiate-ribbed 
Cardita borealis. A few specimens of the translucent Yoldia 
sapolilla have been found, and also several of the almost transparent, 
many toothed leda tenuisculata. 
Passing to. the Mussel family (Mytilidae), the Bay affords at least 
four species, of which far the most abundant is the edible mussel 
i^Mytilus edulis). Crowded closely together above ground and 
clinging by the firm byssus, they occupy great beds, all of a dull 
black color except where a lighter colored specimen of the variety 
pellucidus is more conspicuous than its fellows. The nearer low 
water mark the larger they are, while they are found at their fullest 
perfection by dredging in four or five fathoms. In Gould’s 
Invertebrata of Massachusetts the general length is given as 2 4-10 
inches, but I have found them in abundance 3 1-2 inches long and 
even larger. Closely resembling it, but perfectly distinct in generic 
and specific characteristics, is the large horse-mussel {3Iodiola 
modiolus) . This is a large rough shell, almost invariably having 
attached to it various sea weeds or colonies of bryozoa and corallines. 
In the Invertebrata of Massachusetts it is said to inhabit 
deep water, probably upon a rocky or pebbly bottom. The existence 
of a large and well situated tide pool on Pendleton’s Island has 
enabled me to see the animal under the actual conditions under 
which it lives. At this place the tide leaves, for about an hour, a 
hollow in the rocks of an average depth of about a foot and extent 
of about 900 square feet. Here great numbers of the horse-mussel 
may be found, with its long and tough byssus so firmly fixed among 
the pebbles and small boulders of the bottom that it requires a very 
considerable amount of strength to tear it from its resting place, 
and then the byssus never gives way, but brings up with it the large 
mass of material to which it is attached. It lies about half imbedded 
in the bottom, gaping wide open, while every shell is rough with 
growths of nullipores, bryozoa, lamenaria and other parasite organ- 
isms. 
Among the most delicately marked of our shells, especially when 
seen under a lens of moderate magnifying power, is the small 
Modiolaria nexa^ the massing of the fine lines of the shell forming 
