^D. aculeata^ ("spiny"). Fronds cylindrical at base, flattened above; branches long and straight, arranged alternately, when young beset with pencils of fine hairs, often one half of an inch long, which, later, fall off, leaving alternate spines along the edges of the flattened branches. It [pg067] grows from one foot to six feet in length, below low-water mark, and is found washed ashore. It is an attractive plant in the spring, but is brown and coarse when old. Common everywhere. (Plate X.) ^D. ligulata.^ Fronds two to six feet long, pinnate, having a flat main stem one half of an inch or more wide, with opposite flat branches; leaflets arranged along the edges of the branches, pointed at each end, and bordered with forward-pointing spines. It is found washed ashore, in abundance, in California, but is not found on the Atlantic coast. (Plate X.) GENUS ^Arthrocladia^ ^A. villosa.^ Olive-brown filaments, resembling fine, knotted threads, each knob having a whorl of delicate filaments. It grows from six inches to three feet long, in deep water. It is rare, but is occasionally found on the New England coast. ORDER =DICTYOSIPHONACEÆ= GENUS ^Dictyosiphon^ ^D. fœniculaceus.^ Fronds filiform, bristle-like, branching into delicate, hair-like branches; yellowish-brown. It resembles /Chordaria flagelliformis/, but is much finer. (Plate XI.) ORDER =ELACHISTACEÆ= GENUS ^Elachista^ The plants of this genus are small, olive-colored, unbranched, hair-like filaments, growing in dense, radiating tufts, one half of an inch in height, on /Fucus/. They are interesting to the microscopist, but not to the collector. ORDER =CHORDARIACEÆ= ("/Cord-like/") GENUS ^Chordaria^ ^C. flagelliformis^ ("whip-like"). Firm, leathery, somewhat elastic, slimy strings, six to twenty-four inches long, and twice as thick as a bristle; branches mostly undivided, short or long, irregularly placed on the main axis, and curving inward at the top of the frond; main axis not extending as far as the branches; blackish in color; attached by a disk to stones and shells; solitary or in bunches. It is common along the New England coast. (Plate XI.) [pg068] GENUS ^Mesoglœa^ ^M. virescens.^ Soft, slimy filaments, with branches and branchlets; olive-green. (Plate XI.) ^M. divaricata.^ Fronds two to twenty-four inches high; branching irregularly, and generally without definite main axis; branches flexuous, solid at first, later hollow; branchlets short and wide-spreading. Common from Cape Cod southward; abundant in Long Island Sound. (Plate XI.) GENUS ^Leathesia^