CHILEAN SPECIES OF METZGERIA. 289 



and also scattered over the ventral surface, especially in the median 

 part; calyptra about 2 mm. long and 0.9 mm. wide, more or less hairy 

 throughout but especially in the upper half: gemmae rarely abun- 

 dant, marginal, borne on undifferentiated branches, oblong, flat or 

 nearly so, usually with crowded rudiments of marginal and sometimes 

 paired hairs slightly displaced to one surface. 



Specimens examined: Chile, without definite locality or date, 

 Neger 68 (B., as M. conjugata, and listed under this name by Stephani, 

 19, p. 951); near Santiago, 1882, Philippi 24 (B., as M. furcata, and 

 listed under this name by Stephani, 9, p. 941); Concepcion 1905-06, 

 Thaxter 90, G (H., Y.); San Antonio, Pudeto River, Chiloe, July, 

 1908, Halle & Skottsberg 257 (U., as M. Lcchleri, and listed under this 

 name by Stephani, 24, p. 10). No. 90, collected by Professor Roland 

 Thaxter, may be designated the type; No. 257, from Chiloe, is poorly 

 developed and somewhat doubtful. 



In M. divaricata and the species that follow the structure of the costa 

 is far more constant than in M. frordvpiMs, 31. drcrcscens and M. cor- 

 ralensis. This does not mean that an absolute constancy is to be 

 expected. In M. divaricata, for example, the ventral cortical cells 

 may be in five rows instead of four, even at some little distance from a 

 fork; it simply means that deviations from the typical numbers are 

 infrequent enough to be ignored. 



As noted in the description the ventral hairs vary greatly in abun- 

 dance. In the more extreme development of these hairs the entire 

 ventral surface appears loosely pubescent, and the marginal hairs 

 occur between every two marginal cells. In typical cases these mar- 

 ginal hairs are paired and spread so widely apart that they form a 

 straight line perpendicular to the margin. As a rule the outer hair of 

 each pair is truly marginal and the inner ventrally displaced. Some- 

 times, however, the outer hair is slightly displaced too, and a sem- 

 blance of displacement is often brought about by the slight convexity 

 of the wing-margins. When a long series of these paired and divari- 

 cate marginal hairs is present the thallus acquires a very striking and 

 distinctive appearance (Fig. 4, A). Unfortunately the condition just 

 described is not always realized. Sometimes, for example, one part 

 of a thallus may be pubescent, while other parts produce hairs spar- 

 ingly or not at all. An entire thallus, in fact, may be sparingly hairy 

 throughout, and most of the marginal hairs present may be borne 

 singly. Even under such circumstances, however, a prolonged search 

 will usually bring to view an occasional pair of the characteristic 

 marginal hairs. 



