1915] 



BRITTON VEGETATION OF MONA ISLAND 51 



scurely or sometimes distinctly angled, often flattened, destitute of wing-margins, 

 almost uniformly areolate over the whole surface, with age showing in profile 

 obtuse or truncate papillae 3-5 /a long, areolae mostly 10-18 /* wide. 



On wet, sunny soil, accompanied by R. violacea, between Sardinera and Ubero, 

 Mona Island, February, 1914, Britton, Cowell, & Hess, Hlfta. 



Riccia Brittonii exhibits certain points of contact with Riccia sorocarpa Bisch. 

 and R. dictyospora M. A. Howe. 1 It is close to R. sorocarpa in vegetative char- 

 acters, though differing in the wider, more pronounced, scarious-albescent thallus- 

 margins and slightly in the character of the epidermis, but it departs widely from 

 this species in the spores, which are much larger ( 100-145 /a vs. 70-90 fi, max. 

 diarn. ), are destitute of wing-margins, and commonly have the areolae of the 

 inner faces almost as well and regularly developed as those of the outer face. 

 From Riccia dictyospora, the species differs in the less elongate thallus (2-5 

 mm. vs. 4-10 mm.), the albescent instead of dark purple thallus-margins and 

 scales, the more semicircular and less parabolic outlines of transverse sections of 

 the thallus, and in the larger spores (100-145 fi vs. 95-116 fi, max. diam.), 

 with larger areolae ( 10-18 fi vs. 8-12 fi. 



RICCIA VIOLACEA, sp. nov. 



Thallus simple or 1-3 times dichotomous, irregularly gregarious, 1.5-4.0 mm. 

 long, the main segments oblong-obovate or linguiform, 0.65-1.15 mm. broad, rather 

 obscurely and finely areolate and dark green above, dark violet or blackish at 

 margins and on sides, this color encroaching on the surface here and there, es- 

 pecially in the older parts and at the sinuses; median sulcus shallow or obsolete 

 except at apex; ventral scales very short or rudimentary, dark violet, rarely over- 

 lapping, commonly divided into a series of small irregular often tooth-like lamellae, 

 each consisting of only a few cells; transverse sections plano-convex, somewhat 

 flattened-semiorbicular, or occasionally biconvex, 1.5-2.0 times as wide as high; 

 the margins obtuse or rounded, bearing especially toward the apex numerous 

 or occasional violet or sometimes hyaline conic or subcylindric acute or obtuse 

 papillae 30-110 fi long and 25-45 /x broad at base; cells of the primary dorsal 

 epidermis subhemispheric or mammiform, soon collapsing and leaving inconspicu- 

 ous vestigia; remaining parts unknown. 



On wet, sunny soil, accompanied by Riccia Brittonii, between Sardinera and 

 Ubero, Mona Island, February, 1914, Britton, Cowell, & Hess, 1749b. 



In size, habit, and color, R. violacea is somewhat suggestive of R. nigrella DC, 

 but the thallus has papillae or very short cilia at the margins, which are wanting 

 in R. nigrella, the scales are much smaller, more rudimentary and more divided 

 than in R. nigrella, and the cells of the primary epidermis are much less persistent. 

 Its nearest affinity is doubtless with R. atromarginata Levier, which is known 

 from Sicily, Sardinia, and Greece; from this it appears to differ (if one may 

 judge from the descriptions alone) in the obtuse thallus-margins, the very short, 

 rudimentary, divided, rarely overlapping scales, and the commonly violet papillae 

 which are confined to the margins and sides while in R. atromarginata the hyaline 

 incurved "pili" are said to cover also the anterior dorsal surface. 



LICHENES 

 i 



(Determined by Professor Lincoln W. Riddle) 



ARTHOPYRENIA 



On Coccolobis obtusifolia, Ubero. 



PYRENULA 



On bark, Sardinera. 



MELANOTHECA CRUENTA (Mont.) Muell. Arg. 

 On Gymnanthes, Sardinera. 



TRYPETHELIUM ELUTERIAE Spreng. 



On Pithecolobium, Sardinera, and on Coccolobis obtusifolia, Ubero. 



!Bull. Torr. Bot. Club 28: 163. 1901. 



