8 Rhodora [JANUARY 
The genus is taken here in the restricted sense, including only 
the species having fronds always flat ; those with tubular fronds, some- 
times included in it, now forming the genus Ænteromorpha. About 
six species can be considered as well established, though a number 
of others have been described, some of which must be considered as 
forms or varieties, and others are insufficiently known. U. Lactuca 
is cosmopolitan; U. fasciata is found in nearly all warm seas; U. 
Californica is known from only one station. 
KEY TO THE SPECIES. 
Fronds minute, triangular or reniform, with distinct stipe 2. U. CALIFORNICA. 
Fronds ample, undivided or irregularly lobed I. U. LACTUCA. 
Fronds divided into linear segments 3. U. FASCIATA. 
1. U. Lacruca L. Sp. Pl, 1163, 1753. Frond very variable in 
shape, at first attached and generally of a lanceolate or ovate lance- 
olate form; later of irregular shape, and often detached and float- 
ing. The cells usually vertically elongate in cross section (see 
Plate 41, fig. 1); seen from the surface, irregularly angular, closely 
set; thickness of frond very variable. 
A very common plant over the whole world, and extremely varia- 
ble in form, thickness and color. Two fairly marked types can be 
distinguished in the species as found with us on both Atlantic and 
Pacific coasts, connected by innumerable forms. Farlow (2) 379; 
(3) 713; (4) 42, Pl. III, fig. 1. Hay (1) 33. Hay & MacKay (1) 
63. Collins (3) 310; (6) 77; (7) 246; (8) 45. Dame & Collins 
(1) 157; Bennett (1) 95. Martindale (1) 92. Britton (1) 400. 
Anderson (1) 218.  Rosenvinge (1) 939; (2) 145; (3) 116. 
McClatchie (1) 351. U. Lactuca var. Lactuca Farlow (4) 43. Hay 
& MacKay (1) 63. Martindale (1) 92. Britton (1) 400. Collins 
(7) 246. U. latissima Curtis (1) 156. Harvey (1) 59; (2) 176. 
Kemp (1) 41. Harvey & Bailey (1) 163. Ashmead (2) 96. Olney 
(1) 42. Eaton (1) 348; (2) s. Farlow (1) 292; (2) 379; (3) 
712. Robinson (1) 166. Anderson (1) 218. Fowler (1) 48. 
Var. RIGIDA. (Ag.) Le Jolis, Alg. Mar. de Cherbourg, 38, 1863. 
Frond at first lanceolate or ovate lanceolate, firm and stiff, with a 
distinct stipe; later somewhat irregularly divided, and often with 
numerous perforations of various sizes; cells vertically elongate in 
cross section. Plate 41, fig. 1. cross section. 
This is a common form of exposed shores, but occurs also some- 
times in quieter waters. In its earlier stage it is distinctly lanceolate 
in outline, but this form is afterwards lost by irregular growth. It 
„is firm in texture, the color growing deeper as the plant grows older, 
finally becoming brownish or blackish; the cells have their greatest 
length at right angles to the surface of the frond, being sometimes 
three times as long as wide. Farlow (4) 42. Hay & MacKay (1) 
