[407] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 113 
in Wood’s Hole passage and several other localities on rocky or grav- 
elly bottoms. This was the Cribrella sanguinolenta; it is much more com- 
mon north of Cape Cod, and is abundant in the Bay of Fundy and vorth- 
ward to Greenland ; it is also found on the northern coasts of Europe. 
It has not been found much south of Vineyard Sound on this coast. 
It can easily be distinguished by its five round, tapering rays, covered 
with small spinules, and by having only two rows of locomotive suckers 
in the grooves on the under side of the rays, instead of four rows, as in 
the common star-fishes belonging to the genus Asterias. Its color is 
quite variable. It is often orange, or purple, or rose-color, or cream- 
color, and sometimes mottled with red and purple, &c. Unlike the pre- 
ceding, and most other species of our star-fishes, this does not have free- 
swimming young. Its eggs are deposited around the mouth, and re- 
tained by the mother until they develop into little star-fishes capable of 
taking care of themselves. 
The Hydroids are very numerous on rocky bottoms. A few species, 
like Hydractinia polyclina (p. 328) and the Thamnocnida tenella, attach 
themselves directly to the rocks, but the greater number adhere to as- 
cidians, algze, or to other hydroids. Many of the species are also to be 
found on the rocky shores in tide-pools, and have already been mentioned. 
Among those not yet detected at low water is a delicate species of Plu- 
mularia, with slender, alternately pinnate branches, which was found 
growing upon rocks in company with Hydractinia. The Thamnocnida 
tenella is a Tubularian which grows in clusters, two or three inches high, 
consisting of long, slender, somewhat branched stems, which are more or 
less crooked, and usually irregularly and distantly annulated, with beau- 
tiful pink heads at the top. The general appearance is like that of the 
Parypha, (Plate XXXVI, fig. 274.) The Obelia dichotoma was found grow- 
ing upon ascidians (Cynthia partita, &c.) in 8 or 10 fathoms, among rocks. 
Itis a well-known European species, but has not hitherto been established 
as an inhabitant of our coast. It has dark, horn-colored, slender stems, 
with pretty. long and rather erect, slender, alternate branches, which 
branch again in the same way. The hydroid cells are deeply campanu- 
late, with the margin slightly sinuous or scolloped, the slight notches 
corresponding with faint angular ridges which run down on the upper 
parts of the cells, giving the upper half a slightly polygonal form. In 
this respect this species closely resembles the Obelia commisuralis. The 
reproducsive capsules are elongated, urn-shaped, with a narrow, raised, 
sub-conical neck. 
The Obelia geniculata is often very abundant on the fronds of Lami- 
naria and other alge having flat fronds. Its creeping tubular stolons 
often thickly cover the surface with a complete net-work; from these 
the erect stems rise to the height of about an inch. This species may 
be known by the prominent geniculation at the origin of the hydroid 
pedicels. The Obelia fusiformis has a similar mode of growth, but is 
