4 PROCEEDIIirGS OF THE NATIONAL MUSEUM vol. 81 



The fact that in both of two infested opossums, worms with all the 

 variations described above were found, and that any division of the 

 specimens into two or more species would appear to be purely arbi- 

 trary, leaves little room for doubt that only a single species is rep- 

 resented. Since a single species may show a well-marked division of 

 the body or none at all, and may or may not possess glandular struc- 

 tures, which when present vary astonishingly in appearance, being 

 sometimes in the form of suctorial cups and sometimes in the form 

 of earlike appendages, considerable doubt arises as to the validity of 

 some of the genera into which the old genus Heinistoinmrb has been 

 divided. (See LaEue, 1926.) According to LaRue's arrangement 

 of the genera, this species seems to fit best into Proalaria^ to which it 

 is here assigned, but ProalcuHa may very well have to become a 

 synonj^m of N eodiplostoTnuni. ' 



HARMOSTOMUM OPISTHOTRIAS (Lutz, 1895) 



Specimens that have been referred to this species were found in 

 three out of four opossums examined. The species has hitherto been 

 recorded from another opossum, Didelphis aurita^ in southern Brazil 

 by Lutz (1895) and later by Braun (1899). The descriptions diifer 

 in several respects, but the species seems to be a very variable one, 

 and there seems to be little doubt that the forms described by Lutz 

 and by Braun are cospecific. More recently Dickerson (1930) has 

 described a form that he considered a variety of the same species, to 

 which he gave the name Hamnostonvumi opisthotnas var. virginia- 

 nwn. Dickerson's fluke is markedly smaller in size than the forms 

 described from South America, ranging from 1.535 mm to 2.541 mm 

 in length and from 314/x to 415/a in breadth, whereas Lutz gives the 

 size as 4 mm by 0.9 mm to 1.1 mm, and Braun as 6 mm to 7 mm by 

 0.6 mm to 1 mm. The eggs in Dickerson's specimens, on the other 

 hand, are larger, measuring 16;u, by 31/a, as compared with 14(U, by 27ju, 

 (Braun). Dickerson's specimens have the anterior part of the body 

 provided with blunt rudimentary spines, whereas Lutz describes the 

 body as being spined and Braun as being devoid of spines. It seems 

 likely that this difference may be due to different methods of preser- 

 vation and treatment. 



My own specimens, interestingly enough, bridge the gap between 

 Dickerson's Virginia specimens and the Brazilian forms in so far 

 as size is concerned, since they range from 1.78 mm to 5.33 mm in 

 length and from 314/t to 450/a in breadth. The ratio of length to 

 breadth varies from 1 : 4.4 to 1 : 10.4. In my specimens I am unable 

 to find any trace of spines either in whole mounts or in sections; in 

 this respect the Texas specimens agree with Braun's description of 

 the Brazilian ones. The ventral sucker in the Texas specimens, as in 



