INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 351 



ilar habits, but does not grow to. a very large size. The largest specimens 

 observed are only sis or eight inches loug, 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 fossse of the head are long and 

 deep; the ventral opening is relatively much smaller than in M. irigens 

 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 MecTcelice, 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 Xemertean, 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 subcorneal, 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 fossae, is small, triangular. The 

 color is deep flesh-color or light purplish. 



The Balanoglossus aurantiaous is a very remarkable worm, related to 

 the Xemerteans, 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 Xobska Light, and also at Beverly, 

 Massachusetts. Dr. Packard informs me that he has collected it at 

 Beaufort, Xortk 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 



