250 



THAXTER. — 



MONOGRAPH OF THE LABOULBENIACE^E. 



version to a more primitive structure may be compared, perhaps, to the reversions due to wounds or 

 injuries so often seen in the higher plants. Despite this very common occurrence of Peyritschiella-i brms 

 in probably all the species of Diehomyces, I consider the genus well distinguished by its normally sym- 

 metrical receptacle and paired antheridia, this condition occurring in PeyritschieUa only in exceptional 

 individuals if at all. 



The most striking variation which one finds in the species of Diehomyces is connected with the pres- 

 ence or absence of the two characteristic "auricles" which surmount the tips of the perithecia in certain 

 cases. Although, the presence or absence of such peculiar structures might well be assumed to indicate 

 a specific difference, it is evident that, in some cases at least, there is a dimorphism in this respect; the 

 auricled form being usually smaller than the other, and even occasionally associated with it on the same 

 individual, as in D. hybridus, Plate XXXI, fig. 16. More often, however, as in D. biformis, the two are 

 always separated on distinct individuals, as is shown in Plate XXXIII, fig. 1-3. This circumstance 

 renders the separation of the species a matter of considerable difficulty in many cases. For example D. 

 vulgatus is an auricled form occurring all over the world on various Philonthi, and is associated not infre- 

 quently on the same insect with a variety having no auricles. This variety may be almost, if not absolutely, 

 identical in appearance with the typical D. princeps, a species which is very common and widely distrib- 

 uted on similar hosts, but which I have not found associated with individuals of an auricled type in its 

 typical condition, although it is not infrequently found covering the host in great numbers. The ex- 

 istence of this dimorphism, however, may render necessary the union of these and possibly other forms, 

 although at the present moment I am inclined to consider them distinct. 



The antheridium in this genus, from its position and the usually dark color of the adjacent cells, is 

 not easily examined; but its structure is evidently like that of most compound antheridia; the antheridial 

 cells being seemingly proliferations from a subterminal cell into a terminal cell, which serves as a receptacle 

 for the antherozoids as they are formed, and as a common medium of discharge. These conditions are 

 indicated in a general way in fig. 4, Plate XXXII, but no form has been examined in which more than 

 a very general idea of the cell-arrangement could be obtained. 



The species of the genus are confined to hosts belonging to the Staphylinidae, and are especially com- 

 mon on members of the large genus Philonthus, some of them being more or less general parasites on 

 these insects, while others appear to be somewhat definitely restricted in the matter of hosts. That 

 numerous species exist in addition to those below enumerated cannot be doubted. 



If one disregards the tendency, above referred to, to revert to a Peyritschiella-\ike condition, the 

 genus is more constant in its characters than almost any other, the only variation of importance being 

 associated with those forms in which the symmetry is lost through the production of a single perithecium, 

 as in D. Javanus, Plate XXXII, figs. 1-2. It should be mentioned, however, that in some abnormally 

 developed forms, or where the primary perithecia have aborted through injury or otherwise, secondary 

 perithecia may develop from one or both of the two lower tiers, Plate XXXI, fig. 9, a condition seen 

 occasionally in PeyritschieUa. As may be seen by an examination of the accompanying Plates, the 

 members of this genus, from their symmetrical form and bizarre outline and coloring, are among the 

 most remarkable and striking members of the group. The scale-like habit and appressed growth are 

 striking illustrations of adjustment to their conditions of life on the surface of swiftly running hosts. 



Dichomyces furcifertjs Thaxter. 

 This species, which may be regarded as the type of the genus, occurs on small Philonthi, and is 

 common in New England. Typical specimens were obtained in the British Museum on P. alhipes Grav. 

 from Tillsgate, England, and from P. centralis Sharp, from Las Mercedes, Mexico ? Nos. 364 and 752 re- 

 spectively. It was also found on P. cliscoideus Grav. from Scotland in Dr. Sharp's collection, No. 1212, 

 and it has been obtained in abundance about Fresh Pond, Cambridge. Forms which appear very closely 

 related, if not identical, but varying in minor respects, have also been examined on small Philonthi from 



