BY E. J. GODDARD. 769 



with Astacopsis serratus — an occurrence somewhat analogous to 

 that of Temnocephala on that Crustacean genus. This, I believe, 

 is the only known case of such an association as regards the 

 Oligochista except in the family Discodrilidce, in which we find 

 Branchiobdella on the gills, etc., of Astacus Jluviatilis, and 

 Bdellodrilus on Cambarus; but in these genera there is a state of 

 true parasitism accompanied by special modifications in accord- 

 ance with it, so much so in fact that these forms w T ere once 

 regarded as belonging to the Hirudinea. The peculiar manner 

 of occurrence of this new genus lends some interest to it, inas- 

 much as one reasonably expects the possibility of the existence 

 of some features of special significance in an organism which has 

 adapted itself to such conditions. 



At first I imagined cursorily I had an Enchytrseid genus, on 

 account of the position of the essential genital organs and their 

 pores; but the character of the setse, on detailed examination, 

 and the posteriorly situated spermathecse, place it certainly 

 among the Phreodrilidce. 



Astaco psidrilus, gen.nov. 



Resembling Phreodrilus Beddard, and Phreodriloides Benham, 

 in general as regardsexternal characters and anatomy, but differing 

 from them in having spermathecal structures in segment xiv., 

 almost devoid of musculature, without direct openings to the 

 exterior but communicating with ovisacal structures in segment 

 xiii. 



ASTACOPSIDRILUS NOTABILIS, sp.nOV. 



The specimens were fixed in picro-nitric solution. The results 

 of my investigations were obtained by the examination of entire 

 specimens stained with hematoxylin and mounted in Canada 

 balsam, together with transverse and longitudinal series of 

 sections similarly treated and counter-stained with eosin. 



Body. — The body consists of fifty-three segments, and measures 

 5-5 mm. in length; and 065 in breadth in the middle region of 

 the body, 0-30 at the anterior extremity, and 0*23 at the posterior 

 end. The greatest body-thickness is to be found in the region of 



