ART. 16 HELMINTH PARASITES OF THE OPOSSUM CHATTDLER O 



the Virginia specimens, is consistently smaller than the oral sucker 

 and falls within the range of measurements given by Dickerson, 

 which is far below that given by Braun. In my specimens the 

 pharynx is separated from the oral sucker by a very distinct pre- 

 pharynx, which may be as much as 40ja in length, whereas in the 

 Virginia specimens, Dickerson says, "Anteriorly it [the pharynx] is 

 connected by a very short — almost indistinguishable — gullet with 

 the oral sucker and opens posteriorly directly into the intestine." 

 In most other respects the Texas forms are similar to the Virginia 

 ones, but there is more variation in the anterior extent of the vitelline 

 glands, these frequently reaching to the level of the middle of the 

 ventral sucker at least on one side, and the close size relationship 

 betAveen the ventral sucker and the anterior testis, which Dickerson 

 stresses, does not exist, for the anterior testis is always larger than 

 the ventral sucker. 



It is evident that this species is a very variable one, especially with 

 respect to size. It is possible that the species of intermediate host, 

 which is probably different in the three regions (Brazil, Texas, and 

 Virginia) in which this fluke has been studied, may have some influ- 

 ence on the size of the adults. At any rate, it is evident that the 

 Texas forms to a large extent bridge the gap between the very small 

 Virginia forms and the large ones described from Brazil, and it 

 becomes doul)tful whether Dickerson's forms should be ranked even 

 as a distinct subspecies. 



RHOPALIAS MACRACANTHUS, new species 



Diagnosis. — Body distinctly divided into anterior and posterior 

 portions ; the anterior portion is broader and slightly concave toward 

 the ventral side, and is separated from the posterior portion, just 

 behind the ventral sucker, by a waistlike constriction. The posterior 

 portion is about two and one-half times as long as the anterior. 

 Total length, 4 mm to 4.75 mm, with a maximum diameter of the 

 anterior portion of the body of 0.75 mm to 1 mm and of the posterior 

 portion of 680/x to 900/x. There is a marked difference in the stain- 

 ing reactions of the two portions of the body. When stained with 

 Delafield's acid hematoxylin the anterior portion takes up the stain 

 much more quickly than the posterior part and takes a deep-blue 

 color, while the posterior part of the body stains slowly and takes on 

 a distinctly red color. 



The proboscis sacs are short and end at the level of the pharynx,* 

 they measure about 280/i, to 320/x in length, with a width of about 

 160/i,. The proboscides seem to be exsertible for only a short dis- 

 tance. They are armed with 10 spines each, arranged in a group 

 near the tip of the proboscis, 5 of them ventral and 5 dorsal, and 

 so arranged that when the proboscis is exserted they point in all 



