58 ULVACEiE. 



spinelike, the plant becomes E. ramulosa of authors. I have seen the varieties erecta, 

 ramulosa and dathrata from the American coast. The cells of which the walls of the 

 frond are composed are larger and more quadrate than those of E. compressa ; the 

 surface therefore looks tessellated. 



4. ExTEROMORPHA HopJch'lii, McCalla ; frond excessively slender and byssoid, flaccid, 

 very much branched ; branches feathery, decompound, erect, attenuated, set with minute 

 subulate I'amuli ; cellules large, hyaline, each containing one or two minute grains of 

 endochrome ; the ramuli formed of a single series of such cells. Harv. Phi/c. Brit, 

 tab. 263. 



Hab. In rock pools between tide marks. Greenport, Mr. Hooper, (v. s.) 



Tufts very soft, 3-4 inches long. Fronds very slender and much branched. The 

 frond of this species is composed of much larger and more hyaline cells than in the 

 preceding, and the endochrome is of very minute size in proportion to the cells in which 

 it is lodged. This species occurs also on the shores of England and Ireland ; but is 

 not so common as others of the genus, and appears to be sufficiently characterised by 

 its cellular structure. The ramuli are articulated, like the branches of a Cladophora. 



IV. ULVA. L. 



Frond membranaceous, flat, and leaflike, green. Fructification ; green granules 

 (spores) often arranged in fours, dispersed over the whole frond. 



Under this generic name I still retain the species of the modern genera Prasiola, 

 Ulva, and Phycoseris ; the first of which differs from the second in having its cellules 

 arranged in a most obviously tessellated pattern ; and the last, from either of the pre- 

 ceding, by its membrane consisting of two layers of cells instead of a single layer. 

 The species of the section Prasiola are of minute size, and are found in damp iilaces, 

 on the soil, on old walls and on decaying timber and thatch, &c. ; and no doubt several 

 (such as P. crispa, P. calophrjlla, &c.) occur in America, but I have not received any 

 American specimens. Kiitzing describes a P. mexicana, Lieb. from Mexico, in words 

 which would apply equally to the P. crispa of Europe. 



Sect. 1. Phycoseris ; membrane formed of a double layer of cellules. 



1. Ulva ( Phycoseris) /a.«'irtto, Delile ; frond stipitate, cartilagineo-membranaceous, 

 rioid, cleft into several strapshapod segments, which are undulate at the margin, and 

 irregularly toothed or sinuate. Del. E<jypt, p. 153, t. 58, /. 5. Mont. Alg. Alyer, 

 p. 151, <. l'i,fiy- 1-2. Phycoseris fnsciata ^Kiitz. Sji. Alg. p All . Viva divisa, Suhrf 



