ULVINA. 



[ 791 ] 



UREDINEJ^. 



or tubular, sometimos filiform fronds, com- 

 posed of spherical or polygonal cells, united 

 together firmly into layers, either single or 

 double. Reproduced "by roundish spores 

 formed from the whole contents of cells, or 

 by ciliated zoospores formed in twos, fours, 

 or many in each cell. 



Ulva. Frond plane, simple or lobed, 

 formed of a double layer of closely packed 

 cells, producing zoospores. 



Enterojnorpha. Frond hollow, simple or 

 branched, of a single layer of closely packed 

 cells, forming a sac or tube ; with zoospores. 



Monostroma. Frond flat or saccate, simple 

 or lacerate-lobed, forming a single layer of 

 cells scattered in a homogeneous membrane ; 

 with zoospores. 



Prasiola. Fronds membranous, lacerate- 

 lobed, formed of a single layer of cells in 

 simple or compound lines, or in groups mul- 

 tiples of four. Spores formed from the 

 whole contents of the cells, motionless. 



ScMzof/onium. Fronds filiform, dilated 

 here and there into flat ribands, containing 

 two or four rows of cells ; spores formed 

 from the whole contents, motionless. 



See PKOTODERiiA and Schizomeeis. 



ULVI'NA. See CRYPTOcocCACEiE. 



UMBILIC A'EIA, Fee ( Gp-ophora,Ach.). 

 — A genus of Phyllodei (Lichenaceous li- 

 chens). U. jmstulata gi-ows on rocks in 

 various parts of Britain. It is remarkable 

 for the tubercles or hollow papillae occurring 

 on its surface. The apothecia are flat, at 

 first black, at length tuberculate. Sper 

 mogonia also occur 

 tubercles 



in the form of little 

 containing a nucleus of densely 

 packed sterig-mata, enclosed by a thin black 

 rind. The species in which the disk of the 

 apothecia is concentrically plicate form the 

 proper Gyrcphorce of Ach. ; they occur on 

 momitain-rocks. Several other species, 



BiBL. Hook. Br. Fl. ii. pt. 1. 223; Tu- 

 lasne, Ann. Sc. Nat. 3. xvii. 207, pi. 5. figs. 

 •5-12 ; Schserer, Enum. crit. 25 ; Leighton, 

 Lich. Fl. 142. 



UMBONEL'LA =LEPnALiApt. (Hincks, 

 Pob/zoa, 31G). 



UNILOCULI'NA, D'Orbigny.— A sub- 

 genus of Miliola. 



Char. Shell regular, equilateral, globular; 

 chambers completely embracing, regularly 

 woimd round the axis, one only apparent, 

 this making a complete revolution around 

 the preceding; cavity simple ; ori/ice single, 

 with a tooth. 



In the other genera of the family, each 

 chamber occupies only half the circumfer- 



ence, whilst here it forms a complete circle. 

 One species, U. ImJica (PI. 23. fig. 2). 

 (D'Orb. For. Fos. Vien. 261.) 



URATES. See Uric acid, 



URCEOLA'RIA, Ach.— A genus of Par- 

 meliacese (Gymnocarpous Lichens), included 

 under rarmclia by Fries, but agreeing in 

 almost every particular with Lecanora. 

 U. scritposa, the commonest species, gi'ows 

 on heaths, walls, and rocks. The disk of 

 the apothecia is black, and the border 

 crenated. The spores are cellular or multi- 

 locular (PI. 37. fig. 17). The si^rmogouia 

 are scattered over the thallus, sometimes in 

 the outer wall of the (thallodal) border of 

 the apothecia ; they are veiy inconspicuous, 

 on accoimt of the light colour of their 

 ostiole. 



BiBL. Hook. Br. Fl. ii. pt. 1. 175 ; Tu- 

 lasne, Ann. Sc. Nat. 3. xvii. 172, pi. 4. figs. 

 5-14 ; Schferer, Enum. crit. 85. 



URCEOLARIA, J)ii].= Trichodina pt. 

 U. mitra=^T. mitra. 



URE'A. — This substance occm'S normally 

 in the urine of man and the carnivora, in 

 small quantity in that of the herbivora ; also 

 in the amniotic liquid, and the vitreous and 

 aqueous humours of the eye. Pathologi- 

 cally, it. is found in the blood, dropsical 

 effasions, vomited liquids, and doubtfully in 

 the saliva, the bile, and perspiration. 



When pure, it forms colourless four-sided 

 prisms, sometimes longitudinally striated, 

 and with one or two oblique terminal facets. 

 The crystals are readily soluble in water and 

 alcohol, but not in pure ether. 



When nitric or oxalic acid is added to a 

 solution of urea, the nitrate or oxalate sepa- 

 rates in the crystalline form. 



The nitrate of urea, when rapidly formed, 

 consists of irregularly aggi'egated scaly cvys,- 

 tals (PI. 13. fig. 18c); when more slowly 

 formed, rhombic or hexagonal plates, or 

 distinct prisms (fig. 18 «, b). The crystals 

 of the nitrate of soda (PI. 10. fig. 19) bear 

 some resemblance to those of the lU'ea salt. 



The crystals of the oxalate of urea some- 

 what resemble those of the nitrate, the 

 rhombic formbeing evident. 



BiBL. That of C^HEJiiSTRY, Animal. 



UREDIN'E/E. — The genus Uredo is 

 shown by Tulasne to have no satisfactoiy 

 claim to a distinct existence, since the struc- 

 tures which have represented it appear to 

 be merely a form of tlie reproductive organs 

 common to a number of plants, wliicli, in 

 their most perfect state, represent the genera 

 Ihiccinia, Phragmidium, Uromyces, Sec. 



