134 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



straight or falcate, sharply serrate, especially on the lower side, and the 

 opposing pinna pinnately divided or compound; pinnae nearly at right 

 angles to the axis, apices acute; tetraspores borne in dense ellipsoidal 

 cluster either at the ends of the simple pinnae or on the serrations and 

 tips of the compound pinnae; tetrasporic masses interspersed with mono- 

 siphonous incurved branches; favellae in similar position to the tetra- 

 spores, nearly concealed by the large, incurved, usually serrate divisions 

 of the involucre. 



On algae, especially on stems of Laminaria, below low- water mark. 



Common north of Boston; Thimble Islands, near New Haven, and 

 dredged off Block Island, Prof. Eaton. 



A common and characteristic alga of our northern coast, extending through Green- 

 land to the northern coast of Europe, and also found in the North Pacific. The present 

 species, together with Euihora cristata and Delesseria sinuosa, form the greater part of 

 the specimens collected for ornamental purposes by ladies on the Northern New England 

 coast. P. serrata, when dried, is usually very dark colored, unless it has previously 

 been soaked for some time in fresh water, and it does not adhere well to paper unless 

 under considerable pressure. It cannot be mistaken for any other species growing on 

 our coast. Whether it is a variety of P. plumosa is a question about which writers do 

 not agree, but, although in this connection our form has been kept as a distinct spe- 

 cies, it is highly probable that it is really nothing more than a coarser northern form 

 of P. plumosa. The typical form of P. plumosa is certainly unknown in New England. 

 The type is more slender, and the pinnsB are pectinate, not serrate. The position of 

 the fruit is the same, the principal difference being in the more strongly marked in- 

 volucre of the favellse and in the tetraspores, which are borne on densely fastigiate 

 branches, which have no cortications, and some of which are incurved and project 

 beyond the general sporiferous mass. In P. plumosa the tetraspores are also borne on 

 the tips of monosiphonous branches, but they are not densely conglomerate, nor are 

 the projecting incurved ramuli prominent. The present species is very rare south 

 of Cape Cod, being known in only two localities and in a much reduced form. 



OEEAMIUM, Lyngb. 



(From Kepauiov, a small pitcher.) 



Fronds filiform, dichotomous or occasionally subpinnate, monosipho- 

 nous, composed of a series of large ovate or quadrate cells, with bands of 

 small corticating cells at the nodes, and in some species also extending 

 over the internodes; antheridia forming sessile patches on the upper 

 branches; tetraspores tripartite, formed from the corticating cells; 

 cystocarps (favellae) sessile at the nodes, usually involucrate. 



A universally diffused and easily recognized genus, of which, however, the species 

 are by no means easily recognized. The genus is distinguished by the monosiphonous, 

 dichotomous frond, with bands of small corticating cells at the nodes, or, in some cases, 

 covering the internodes as well The tips of the filaments are forked and usually de- 

 cidedly incurved, whence the generic name is derived. The apical growth and forma- 

 tion of the cortex is fully detailed by Nsegeli and Cramer in Pfianzenphysiologische 

 Untersuchugen, Part IV. The procarp in Cerammm is furnished with two trichogynes 

 and a single earpogenic-cell formed from the cortical cells on the convex side of the 



