POLVZOA. 241 



lipora and Idmoneu are common in the shallow waters north of Cajju Cod, one species 

 of tlie foi'mor srenns exteiulintr to tlie sonth of tliat hari-ier. 



SuB-OiiuER II. — Ctenostomata. 



Here the cell is closed, after the retraction of the polyjiide, by processes of the 

 tentacular sheath, or by bristle-like projections. Two families, represented by several 

 species, occur on our coasts. In the Alcyoxidiid^ the colony forms a fleshy or mem- 

 braneous mass very irregular in form. Our most common species is Alcijouidimn 

 hiiipidnm, and scarcely less frequent is the closely related A. hlrsutam. These forms 

 are found most abundant surrounding the stems of the rock-weed {Fucus), between 

 tide-marks. The former is thicker, and may be readily recognized by the slender 

 reddish bristles which surround the mouth of the cells. In the second species each 

 cell forms a small soft papilla, from the centre of which the polypide protrudes itself. 

 A. ramoswn is a large branching species, which not infrequently forms colonies over 

 a foot in length, the branches sometimes being nearly half an inch in diameter. In 

 the Vesciculaeid^e the general form of the colony is a creeping or upright brandl- 

 ing mass, from which the cells arise as free sheaths. In Vescicularia these sheaths are 

 sessile upon the stock, while in FurcHa they are seated upon short peduncles. Several 

 species of the former are common upon our coasts, while Farellafamiliaris, which 

 extends from Long Island Sound to Europe, is found on rocks and sea-weed. "When 

 it surrounds the stems of small algaj, the whitish pedicels project outwards, in all di- 

 rections, and thus produce the appearance of a delicate chenille cord." Tlie members 

 of the family Paludicellid.e are inhabitants of fresh water. 



Sub-Okdeu III. — Chilo.stomata. 



The Chilostomata are characterized by having the muulh of the horny or calcareous 

 cell capable of being closed by a lid, while the or.il area is usually membranous, i-ather 

 than hornj^ It is in this group alone that we meet with the vibracula and avicularia, 

 which we have already described, but their presence is not universal. It is divided 

 into four super-families, the lowest being the CELLULARINA. Here the horny or 

 slightly calcareous cells are tubular, funiiel-shaped, the lower attached 

 extremity being tubular or conical. In ^Fta anguinea, which may be 

 taken as the type of the family .^Etid^e, the tubular cells, with the mouths 

 at the ajiex, arise from a creeping root-stalk, while in Eucrate chel((fa, 

 representing the Euceatid.e, the mouth of the cell is one side of the 

 extremity, and the cells are arranged in a single row. In Gemellurid 

 loricata, a large form common in shallow water north of Cape Cod, we 

 have a close similarity to the last species, except that the cells are 

 arranged in pairs, back to back. In the Eucratida? no vibracula or 

 avicularia are present, while in the Cellulaeid.e these structures are fio. iw. — om 

 usually found. The colony branches dichotoniously, and the cells are 

 arranged in two or inore rows. It is represented in our waters by sjiecies of Celhi- 

 laria and Cuberea. 



In the BiCELLAEiD.E the cells are conical or quadrangular, and the large, laterally 

 placed mouth is placed near the median axis. Our most prominent species of this 

 family belong to the genus Bugida. Here the branches are arranged in a spiral, giving 



VOL. I. — 16 



