1355] 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 Bittium nigrum (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 XXII, 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 Fulgur carica (Plate XXII, fig. 124) and of Sycotypus canalicu- 
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 repiform, yellowish capsules, parchiwnent- 
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 
