[355] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 61 



and burrows like the last, but this species has its proper home on the 

 muddy shores and in estuaries, and will, therefore, be mentioned again. 



At certain times, especially in the spring, multitudes of the young 

 shells of Blttium nigmim (p. 305, Plate XXIV, fig. 154) are found 

 creeping on the surface of the moist sand in sheltered places, at low- 

 water, and generally associated with large numbers of the Astyris lunata, 

 (p. 306, Plate XXII, fig. 110.) But this is not the proper habitat of 

 either of these species; the reason of this habit is not obvious, unless 

 they may have been accidentally transported to such places. They may 

 be found, however, on the eel-grass growing on sandy shores. The 

 Lacuna vincta (p. 305, Plate XXIV, fig. 139) also frequently occurs on 

 eel-grass and sea- weeds in such places. 



The Crepidula fornicata (Plate XXIII, figs. 129, 129a) and C. ungui- 

 formis (Plate XXIII, fig. 127) occur on shells inhabited by the hermit 

 crabs as well as on the living shells of oysters, Pecten, Limulus, &c ; and 

 the smaller and darker species, C. convexa, (Plate XXIII, fig. 128) occurs 

 both on the eel-grass, and on the shells of Ilyanassa obsoleta, especially 

 when occupied by the small hermit-crabs. Occasionally specimens 

 of Fulffur carica (Plate XXII, fig. 124) and of Sycotypus canaUcu- 

 latus are found crawling on sandy flats or in the tide pools, espec 

 ially during the spawning season, but they do not ordinarily live in 

 such situations, but in deeper water and on harder bottoms off shore. 

 The curious egg-cases of these two species are almost always to be found 

 thrown up by the waves on sandy beaches. They consist of a series of 

 disk-shaped, subcircular, or reniform, yellowish capsules, parchinent- 

 like in texture, united by one edge to a stout stem of the same kind of 

 material, often a foot and a half or two feet in length. The largest 

 capsules, about an inch in diameter, are in the middle, the size decreas 

 ing toward each end. On the outer border is a small circular or oval 

 spot, of thinner material, which the young ones break through when 

 they are ready to leave the capsules, each of which, when perfect, con 

 tains twenty to thirty, or more, eggs or young shells, according to the 

 season. 



Dr. Elliott Coues, who has observed F. carica forming its cases at 

 Fort Macon, North Carolina, states that the females bury themselves a 

 few inches below the surface of the sand on the flats that are uncovered 

 at low-water, and remain stationary during the process. The string of 

 capsules is gradually thrust upward, as fast as formed, and finally pro 

 trudes from the surface of the sand, and when completed lies exposed 

 on its surface. The string begins as a simple shred, two or three inches 

 long, without well-formed cases ; the first cases are small and imper 

 fect in shape, but they rapidly increase in size and soon become perfect, 

 the largest being in the middle ; the series ends more abruptly than it 

 begun, with a few smaller and less perfect capsules. The number of 

 capsules varies considerably, but there are usually seventy-five to 

 one hundred or more. At Fort Macon Dr. Coues observed this species 



