V. SQUAMARIEJ^. 129 



fructification is yet too imperfectly known to enable us to declare Avhctlier the 

 connection be one of analogy or of affinity. Of the eight genera placed liere by 

 Prof J. Agardh, tlie sporiferous nucleus is known only in one. It is therefore 

 premature to say much of the natural character of the Order. 



The plants here associated are either gelatinous, cartilaginous, coriaceous or mem- 

 branaceous expansions, more or less completely attached by their under surfaces to 

 the substances on which they grow. Some few are parasitic on other Alga?, but the 

 greater number adhere to rocks and stones either in the sea or in fresh water streams 

 or rivers. The crust is irregularly or])icular, enlarging by successive additions to its 

 margin, and in the membranous genera is sometimes furnished with concentric lines 

 of growth. In the least developed genus {Actinococcus) the whole frond, scarcely 

 more than a line in diameter, is globose, composed of moniliform filaments set in 

 transparent gelatine, and radiating from a common base. Of this type two species^ 

 parasitic respectively on Chondriis crispus and Phyllophora Broduvi, and which may 

 therefore be expected to occur on the North American coast, have been described. 

 Petrocelis and Cruoria form widely expanded, skin-like patches of a firmly cartila- 

 ginous substance, and dull purple brown or occasionally olive green colour, on the 

 surface of rocks and stones between tide marks in Northern Europe. Like Actino- 

 coccus they consist of beautifully beaded strings of cells set in gelatine. Hilden- 

 hrandtia forms thinner and more decidedly membranous, red, or brown-red skins, 

 sometimes merely films, on stones and pebbles, and differs from the preceding as 

 well by the much denser structure of the frond as by having tetraspores lodged in 

 minute cavities indicated by dotlike pores scattered over the surface of the crust. 

 In its structure and in this fructification there is some aflinity with Melobesia, but it 

 wants the deposit of carbonate of lime which distinguishes that genus. 



Some or all of the genera just named are probably represented on the North 

 American coast, but in the absence of positive evidence of the fact I can do no more 

 than request the attention of collectors to them. They are all obscure looking, 

 unattractive plants, which may easily escape detection. 



I. PEYSSONNELIA. Dm. 



Frond membranaceous or coriaceous, horizontally expanded and rooting by fibrils 

 emitted from the lower surface, composed of two strata of cellules ; the lower 

 stratum of horizontally elongated, cylindrical cellules disposed in radiating fila- 

 ments cohering laterally into a membrane ; the upper of vertically elongated 

 cellules, also arranged in concrete filaments at right angles with those of the loAver 

 stratum. Fruit of both kinds lodged in superficial warts composed of vertical 

 confervoid filaments. Spores I'oundish, in moniliform strings. Tetraspores oblong, 

 cruciate. 



VOL. IV. — ART. 5. 



