[351] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 57 
ilar habits, but does not grow toa very large size. The largest specimens 
observed are only six or eight inches long, and about a fifth of an inch 
broad. The body is also more cylindrical, the flattened part being rel- 
atively thicker and narrower, and not thin at the edges; in contraction 
it becomes nearly cylindrical. The lateral fosse of the head are long and 
deep; the ventral opening is relatively uch smaller than in Mf. ingens 
and usually round. The proboscis is very long, slender; color, light 
purplish red or rose-color. The integument is rather firm and secretes 
a tenacious mucus to which a thin coating of sand often adheres when 
the worms are taken from their burrows. This species seems to con- 
struct an imperfect tube by slightly cementing the sand with its mucus. 
' All these species of Meckelia when caught and when kept in confine- 
ment generally break off portions from the posterior part of the body, 
one after another, until nothing but the head and a lot of short segments 
remain. Under favorable conditions they would doubtless be able to 
restore the lost parts, for other Nemerteans, having the same habit, are 
known to do so, and in some cases even the small fragments from the 
central parts have been known to again become entire worms. Various 
fishes feed upon these Meckelie, and it is probable that the habit of dis- 
membering, or rather disarticulating themselves, may serve an impor- 
tant purpose, by enabling them to escape, in part at least, when seized 
by fishes or crabs, for if even half the body should be lost the remaining 
half would be much better than nothing, for it could soon restore either 
a head or a tail. 
Another Nemertean, which lives in sand at low water, is the Tetra- 
stemma arenicola V., (Plate XIX, fig.98.) This is slender, subcylindrical, 
and four or five inches long when extended. The head is versatile in 
form, usually lanceolate or subconical, and has four eyes on the upper 
side. There is a deep fossa on each side of the head. The ventra 
opening, which is behind the lateral fosse, is small, triangular. The 
color is deep flesh-color or light purplish. 
The Balanoglossus aurantiacus is a very remarkable worm, related to 
the Nemerteans, which lives in the clear, siliceous sand near low-water 
mark. It is gregarious in its habits and occurs abundantly in certain 
spots, although not to be found in other similar places near by. It 
makes tubes or holes in the sand, twelve or fourteen inches deep, and 
lined with a thick and smooth layer of mucus. It throws out of the orifice 
peculiar elliptical coils of sand, by which the nature of the occupant 
may be known. This species was found by our party on the shore of 
Naushon Island, but Mr. A. Agassiz has found it abundantly at New- 
port, and on the beach just beyond Nobska Light, and also at Beverly, 
Massachusetts. Dr. Packard informs me that he has collected it at 
Beaufort, North Carolina, and I have received specimens found at Fort 
Macon, from Dr. Yarrow. The specimens first discovered were found at 
Charleston, South Carolina, by Dr. William Stimpson, twenty years ago, 
but they were only briefly and imperfectly described by Mr. Girard, at 
