255] NORTH AMERICAN MONOSTOMES 37 



comparison with specimens of Cyclocoelum mutabile obtained from the 

 Gottingen museum demonstrates clearly that this is a distinct species. 

 It is similar to Cyclocoelum mutabile in the size and form of the body, in 

 the lateral extent of the uterine loops, the extent and development of the 

 vitellaria, the size of the ovary, and the size and shape of the eggs. 



It differs from this species in having a much smaller pharynx, a much 

 larger sucker, a longer esophagus, larger testes, and a relatively heavier 

 and more irregularly folded uterus. This species is similar to Cyclocoelum 

 prohlematicum Stossich in the size of the testes and the extent of the 

 vitellaria but differs from that species in having a smaller pharynx and a 

 broader, thinner and less muscular body in proportion to its length. For 

 comparison with this species a figure (Fig. 3) of Cyclocoelum mutabile 

 (Zed.) is placed beside that of Cyclocoelum leidyi. 



CYCLOCOELUM PSEUDOMICROSTOMUM nov. spec. 

 [Figures 4, 27, 30, 43] 



Large monostomes 13 to 14.5 mm in length by 4 to 4.5 mm in greatest 

 width which is found at the beginning of the posterior body third. From 

 this point forward the side walls taper gradually to the end of the anterior 

 body third, at which point they bend inwardly more sharply to form a small 

 obtusely rounded end. The posterior end is bluntly rounded. The mouth 

 is subterminal, surrounded by an external banding musculature which 

 measures 662 to 745 ju in diameter. This is followed by a large heavy 

 slightly elongate pharynx 778 to 910ju in length by 745 to 844/i in width. 

 The genital pore lies median and ventral to the forward end of the pharynx. 

 From this point the cirrus pouch stretches posteriad almost to the posterior 

 wall of the intestinal bifurcation. The vitellaria extend from the posterior 

 end of the cirrus pouch to the excretory bladder in the posterior end of the 

 body. It is even more strongly developed than that of Cyclocoelum 

 microstomum and in its lateral extent passes the inner wall of the crura and 

 over the lateral folds of the uterine loops which in this species rarely pass 

 over the inner wall of the crura. The testes as in other species of this genus 

 lie in the posterior region of the body and within the intestinal crura. The 

 posterior testis does not fill the entire intestinal arch, is antero-posteriorly 

 flattened and measures 827 to 910m in width by 993 to 1192)u in length, 

 while the anterior testis which is separated from it by uterine loops meas- 

 ures 745 to 993 ;u in width by 1076 to 1324/x in length. The ovary lies on 

 a level with the anterior margin of the posterior testis and adjacent to the 

 cecum opposite to the anterior testis, is much smaller and spherical, 

 measuring 413 to 496;u in diameter. Dorsal to the ovary is the spherical 

 receptaculum seminis 148 to 165 /x in diameter. The shell gland is similar 

 in size to the ovary and occupies a position dorsal and posterior to that 

 structure. As was stated above the uterus does not usually pass over the 



