1920] Setchell-Gardner : Chlorophyceae 183 



custom, with such information as we may glean from the literature. 

 The Ccniferva riparia Roth was known to Dillwyn (1809, p. 69, under 

 no. Ill) by an authentic specimen in Turner's herbarium. Dillwyn 

 says that the English plants referred by him to Roth's species and 

 figured under the name were treated so on authority of an authentic 

 specimen. Dillwyn figures (loc. cit., pi. E) a plant which has shortly 

 fiexuous, but not contorted, filaments and frequent rhizoidal branchlets 

 of several segments each. Harvey (1849, pi. 238) figures a similar 

 plant which he states is certainly that of Dillwyn, since it is drawn 

 from a specimen belonging to Miss Ilutchins (from Bantry Bay) 

 referred to by Dillwyn. The type of Rhizoclonium riparium (Roth) 

 Kuetz., then, may be properly inferred to be the variety with frequent 

 and complex rhizoids which Rosenvinge (1893, p. 913) named var. 

 polyrhizum. This is certainly a Rhizoclonium, being provided with 

 the rhizoidal branches characteristic of the genus. In general the 

 various authors agree that the diameters of the segments vary from 

 20/^ to 35ju,, but most commonly are from 20/i, to 25^. 



It seems best to us to keep Rhizoclonium ripariutn as thus char- 

 acterized distinct and separate from other varieties (than polyrhizum) 

 usually referred to it. The var. implexum (Dillw.) Rosenvinge, while 

 very similar to the type of R. riparium in both texture and diameter 

 of its filaments, is to be distinguished by the scarcity and structure 

 of the rhizoidal branchlets and is treated here as a distinct species. 

 The Rhizoclonium riparium var. validum Foslie (1890, pp. 138, 139) 

 is decidedly coarser than the type and is probably to be separated 

 from R. riparium in the more restricted sense, although probably 

 closely related to it. 



2. Rhizoclonmm implexum (Dillw.) Kuetz. 



Filaments simple, 20-30/x, (rarely 40/;t) in diameter, yellowish or 

 light green, forming a horizontal fleecy layer; segments 1.5-2.5 times 

 as long as broad; rhizoidal branches few or wanting, when present 

 short, non-septate and usually continuous with the segments from 

 which they arise. 



Forming fleecy masses on mud or on various objects in the littoral 

 belt. Alaska to central California. 



Kuetzing, Phyc. Germ., 1845, p. 206 (at least as to plant of Dill- 

 wyn) ; Batters, Alg. Clyde Sea Area, 1891, p. 230, repr., p. 8. Con- 

 ferva implexa Dillwyn, Brit. Conf., 1805, p. 46, pi. B ; Harvey, Phyc. 



