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84 THE MARINE ALGÆ OF NEW ENGLAND. Var. DENSA. Fronds six to eight inches long, main axis densely clothed with very numerous short branches. Common on stones near low-water mark along the whole coast. The var. densa at Gloucester, Mass., Mrs. Davis. A common species, recognized by its tough, somewhat elastic substance, and reminding one of bunches of small leather shoe-strings. When soaked in water it gives out a large amount of slime, and is not easily mounted. To the naked eye it resembles some of the forms of Dictyosiphon, but the microscopic structure is very different. The variety has been collected several times at Gloucester, but has not been received from other localities. MESOGLOIA, Ag. (From µεσος [mesos], the middle, and γλοιος [gloios], slimy.) Fronds olive-brown, gelatinous, filiform, branching; axial layer composed of filaments rather loosely united into a solid mass, which soon becomes fistulose; peripheral layer of short horizontal filaments, packed in a gelatinous substance; unilocular sporangia oval, borne at the base of peripheral filaments; plurilocular sporangia unknown. The old genus Mesogloia has been divided by modern algologists into a number of genera. In the present instance we have kept in Mesogloia the species in which the peripheral filaments are not transformed into plurilocular sporangia, and have placed in Castagnea the species in which they are so transformed. The distinction between Mesogloia and Castagnea is artificial, because the plurilocular sporangia of Mesogloia proper are unknown, and it is not impossible that they may be formed from the peripheral filaments themselves, as in Castagnea. The development of the fronds is not well known, and the genera founded upon the variations in the mature fronds in the present group are plainly artificial. As regards its development, M. divaricata resembles very closely C. virescens. From a disklike expansion, composed of a single layer of cells, which form spots on the substance upon which it is growing, arise vertical filaments, which end in a hair such as is found in Ectocarpus and other Phæosporeæ. The vertical filaments produce, usually only on one side, fasciculated branches terminated by a hair, beneath which is a cluster of short moniliform filaments. Besides these there arise, at a later period, rhizoidal filaments. The mature fronds of the two species above named may be regarded as a collection of filaments with a trichothallic growth, which have become twisted together and partially united by means of the rhizoidal filaments, and whose fasciculated branches constitute what, in the mature plant, seems to be a distinct cortical layer. In Castagnea virescens the separate filaments, with their lateral fasciculate branches, can easily be isolated by dissecting the smaller branches, and the same thing can also be accomplished with Chordaria divaricata, although not so easily. The species of Mesogloia and Castagnea should not be dried under too heavy pressure, and alcoholic specimens are much better for study than those mounted on paper. M. DIVARICATA, Kütz. (Chordaria divaricata, Ag.; Phyc. Brit., Pl. 17; Ner. Am. Bor., Vol. I, Pl. 11 a.) Fronds tufted, lubricous, six inches to two feet long, branching very irregular, generally without a definite main axis; branches flexuous, ultimate branches very numerous, short, and divaricate, at first solid,
REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 85 afterwards becoming fistulose and tubular; peripheral filaments short, few-celled, the last cell obovate and several times-larger than the other cells; unilocular sporangia ovoid. On algæ and stones near low-water mark. Very common from Cape Cod southward; Niles Beach, Gloucester, Mass.; Europe. A characteristic species of Long Island Sound, where it is probably more abundant than in any other part of the world. It abounds in still, shallow bays. North of Cape Cod it is of small size, and is only occasionally met with. It assumes a number of different forms, none of which, however, can be considered as distinct varieties. It first appears in May, and reaches perfection in August and September. At first the fronds are small and solid, but they grow to be two feet long, or even longer, and the main branches become hollow and finally collapsed. Except that they are more luxuriant, our forms agree well with Norwegian specimens. M. VERMICULARIS, Ag.; Phyc. Brit., Pl. 31. Fronds tufted, gelatinous, one to two feet long, branches long, irregularly pinnate, thick, vermiform, flexuous; peripheral filaments clavate, somewhat incurved, moniliform cells spheroidal; unilocular sporangia ovoid. On stones and algæ between tide-marks. Halifax, N. S., Harvey; Europe. A rather common plant of Europe, and probably occurring within our limits, but as yet only reported at Halifax on the American coast. The species is rather thick and clumsy, and very gelatinous; not at all likely to be confounded with M. divaricata, which is less gelatinous, has a different mode of branching, and whose peripheral filaments are terminated by a cell much larger than the others. Dried specimens may be mistaken for Castagnea virescens, a more slender plant, with longer and more slender peripheral filaments, the upper cells of which are transformed into plurilocular sporangia. We have only examined dried specimens of this species. CASTAGNEA, (Derb. & Sol.) Thuret, emend. (In honor of Louis Castagne, a French botanist.) Fronds and unilocular sporangia as in Mesogloia; plurilocular sporangia formed by outgrowths from the uppermost cells of the peripheral filaments. C. VIRESCENS, (Carm.) Thuret. (Mesogloia virescens, Carm., in Phyc. Brit.; Ner. Am. Bor., Vol. 1, Pl. 10 b; Ann. Sci. Nat., Ser. 3, Vol. 14, Pl. 27.) Pl. 7, Fig. 1. Fronds filiform, gelatinous, three inches to a foot and a half long, axis clothed with numerous, irregular, flexuous branches, ultimate branches short, given off at wide angles; fronds at first solid, becoming fistulous; peripheral filaments slender, clustered, recurved or incurved, cylindrical or only slightly moniliform, cells ellipsoidal, .015-20 mm in diameter; unilocular sporangia ovoidal or rhombic-ovate; plurilocular sporangia
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