CONTRIBUTIONS FROM THE CRYPTOGAM IC LABORATORY OF 



HARVARD UNIVERSITY. 



LXXL— PRELIMLNARY DESCRIPTIONS OF NEW SPECIES 

 OF RICKIA AND TRENOMYCES. 



By Roland Thaxter. 



Received August 19. 1912. 



RiCKIA. 



The genus Rickia has proved to be a large and varied one, and 

 although I have enumerated below only those forms parasitic on 

 Acari which have come under my notice, many others are known to 

 me on a variety of hosts, an account of which I have reserved for a 

 future paper. The general habit appears to be very variable, includ- 

 ing in addition to the condition seen in the type form, others in which 

 the median cell-series is undeveloped, as well as various species with 

 a more or less complicated system of branches. The antheridial 

 characters, moreover, appear to be equally variable. Not only do 

 the antheridia which are extraordinarily abundant in some species 

 seem wholly lacking in others, but their character may vary in differ- 

 ent cases. In some there may be a single antheridium, only, similar 

 to that of PeyritschieUa, definitely placed at the base of the perithe- 

 cium; or an antheridium of this type may be associated with others 

 of the normal habit variously disposed. Again even in forms having 

 the three characteristic cell series, antheridia may be present like 

 those of the genus formerly separated as Distichomyces, each anther- 

 idial cell becoming more or less free in a compact group. Since both 

 the antheridial characters and those of the receptacle thus appear to 

 be so variable, it has not seemed desirable to limit the genus to the 

 type form as illustrated by Rickia Wasvianni, and I have therefore 

 given it a more liberal interpretation; including under it forms with 

 two or with three cell-series, whether they be simple or branched, and 

 whether their antheridia be of the Rickia or the Distichomyces 

 type. The latter genus is, therefore, abaiuloned, one species only, 

 Rickia Leptochiri, being involved in- this change. 



