362 BULLETIN 140, UNITED STATES NATIONAL MUSEUM 



KEY TO SPECIES OP ANCYRACANTHOPSIS 



Male 3.5 to 4 mm., female 5 to 6 mm. long; vulva in posterior part of body; 



in Sterna risoria Ancyracanthopsis bihamata, p. 362. 



Male 7 mm., female 9 mm. long; vulva slightly posterior to middle of body, 



dividing body length in ratio of 4 : 3 ; in Eurypyga helias. 



Ancyracanthopsis bilabiata, p. 362. 



ANCYRACANTHOPSIS BILABIATA (Molin, 1860) Diesing, 1861 



Synonym. — Ancyracanthus bilabiatus Molin, 1860<i. 



Host. — Primary : Eurypyga helias; secondary : Unknown. 



Location. — Between tunics of gizzard. 



Morphology. — Ancyracanthopsis (p. 361) : Body attenuated an- 

 teriorly, densely striated transversely. Head with 4 pinnate append- 

 ages which are larger in the male than in the female. 



Male 7 mm. long. Caudal extremity twisted twice in spiral. Cau- 

 dal alae wide, papillae short. One spicule long and filiform, the 

 other short, thick, navicular. 



Female 9 mm. long. Caudal extremity twisted in spiral, apex 

 obtuse, depressed in center. Anus not far from posterior extremity. 

 Vulva in posterior part of body, prominent, bilabiate. 



Life history. — Unknown. 



Distribution. — South America (Brazil). 



ANCYRACANTHOPSIS BIHAMATA (Mueller, 1897) Cram, 1927 



Synonym. — Ancyracanthus bihamata Mueller, 1897. 



Host. — Primary: Sterna risoria; secondary: Unknown. 



Location. — Between tunics of gizzard. 



Morphology. — Ancyracanthopsis (p. 361) : Body threadlike, with 

 fine transverse striations. Anterior part of body (fig. 424 a and b) 

 diminished gradually or sometimes suddenly to one-fifth the average 

 thickness. Mueller states that this anterior part of body is appar- 

 ently capable of extension and retraction ; the esophagus in this sec- 

 tion is very convoluted. Head with 4 posteriorly directed pointed 

 processes, 23 to 40/x long, similar to those of A. bilabiata. In addi- 

 tion, at the ba*se of the large processes the head bears a crown of 

 smaller papillae or projections, apparently 8 in number, sometimes 

 resembling the larger ones in form. Esophagus in 2 parts. 



Male 3.5 to 4 mm. long by 170 to 180/* wide. Caudal extremity 

 (fig. 424 c and d) rolled in loose spiral. Caudal alae long and nar- 

 row, but thick; 6 pairs of preanal, 5 pairs of postanal papillae along 

 the margin and, in addition, in the median field at the posterior ex- 

 tremity a pair of small papillae and anterior and posterior to this 

 pair, there is a pair of small knobs. Spicules unequal, the right (fig. 

 424 e) IOO/a long, ending in 3 fine points, the left 34/x long and, ac- 



