706 THAXTER. 



developed, the apex more often bearing a variably developed ' trigger- 

 appendage.' 



More than a dozen forms of this type are known to me from the 

 Eastern as well as the Western Hemisphere, all of which are parasitic 

 on species of the dipterous genus Ilyfhea. The type appears to be 

 so constant in the not inconsiderable number of forms already known, 

 that I have concluded to separate it generically from any of the spe- 

 cies of Corethroviyces, which is its nearest ally, although some of the 

 members of this genus may bear free single antheridia. In the 

 present instance the antheridia arise in usually divergent pairs from a 

 small special cell, androphorous cell, separated distally on the inner 

 side, from the subbasal cell of the appendage. This condition which, 

 with slight modifications, is characteristic of all the species, is the 

 principal basis for this separation, but it is well to bear in mind that it 

 may prove an insufficient one, when more species have been accumu- 

 lated. It differs from the nearly allied Rhizomyces, a genus also 

 characteristic of dipterous hosts, in the general type of its appendage, 

 the position of its branches, and especially of the antheridia, both 

 being external in relation to the axis of the appendage. 



The identity of the axis-cells of the appendage in IlytJieomyces, 

 especially of the terminal ones, is generally lost; owing to the deep 

 suffusion of this region, as well as to the fact that the distal ones, as 

 they are formed, appear to undergo a threefold proliferation; the 

 distal proliferation forming the next axis-cell above; or, if it is the last 

 of these cells, forming a terminal branch; while the other two pro- 

 liferations form the superior and inferior branches, respectively. 

 The terminal axis-cell is thus little more than the point of union of 

 three branches, one terminal, one superior and one inferior. The 

 blackened base of the appendage in all the species, appears to be in 

 contact with three cells, the basal and subbasal cells of the receptacle 

 and the stalk-cell of the perithecium. The ascogenic cell is solitary, 

 where the number has been determined, and the four regions of the 

 perithecium proper are usually not definitely differentiated, with the 

 exception of the apex, which may be very clearly distinguished. 



In a majority of the species the basal cell is very small, and so com- 

 bined with the foot, that it is more or less indistinguishable from it, 

 except for its hyaline upper margin. 



Among the species herewith enumerated, /. elegans has the most 

 highly developed appendage and is taken as the type. I. anomalus on 

 the other hand, is the simplest, and is peculiar for several reasons, 

 notably in bearing a single antheridium, only, from its androphorous 



