261] NORTH AMERICAN MONOSTOMES 43 



Brandes (1892) enumerates this among other species which he has 

 not had opportunity to study and he justly says that it is inadequately 

 described. Monticelli (1892) and Braun (1893) in spite of the meager 

 description retain it as a valid species. 



The original material of this species is found in the Army Medical 

 Museum under Number 1035 Comparative Anatomy Series with the 

 description "Flukes Monostomum obscurum from the stomach of a Jew- 

 fish (Stereolepis)." From this I have written the following description. 



Monostomes of medium size measuring from 6 to 13 mm in length and 

 from 1 . 5 to 3 mm in maximum width which is found a little posterior to 

 the middle of the body. The margins of the body are almost parallel for 

 the greater part of their length, tapering gently to the more pointed 

 anterior end and abruptly to form the obtusely rounded posterior end. As 

 in most species of this genus the body is convex dorsally and flat or slightly 

 concave ventrally. The sub terminal mouth is surrounded by a weakly 

 developed sucking musculature which measures 115/z in diameter. This 

 leads to the spherical or slightly elongated pharynx, measuring 115 to 

 264 ju in width by 115 to 298 ju in length. Following this the slender esopha- 

 gus, 500 to 750/z in length, leads to the intestinal bifurcation. The crura 

 are quite variable in size as well as in the character of the median wall. 

 In some cases they show a tendency to the formation of internal ceca; these 

 appear to be due to the pressure from the closely packed uterus which fills 

 the space between the crura. The excretory system in this species has not 

 been made out except for the single termnal excretory vesicle situated as 

 in the other species of this genus between the posterior arch of the intes- 

 tinal crura and the posterior body wall. It opens to the exterior by a single 

 dorsal pore. The genital organs lie within the intestinal crura in the 

 posterior end of the body. The posterior testis, filling the posterior arch 

 of the intestine, is flattened anteriorly by the closely packed uterine 

 loops and is slightly larger than the anterior being 300 to 877 n in width 

 by 480 to lOOOju in length. The anterior testis is usually more nearly 

 spherical and measures 380 to 827/x in width by 462 to 827/i in length. 

 It lies obliquely anterior to the posterior and adjacent to the crura. The 

 vasa efferentia are short and unite a short distance anterior to the anterior 

 testis to form the vas deferens which for the most part passes dorsal to the 

 uterus to the cirrus pouch. This organ is of medium size 248 to 579/i in 

 length by 115 to 199 ju in width. In general its posterior limit lies on a 

 level with the middle of the intestimal bifurcation. The ovarian complex 

 lies between the testes and on the side opposite to the anterior testis. 

 It is composed of a spherical ovary, 275 to 463 /x in diameter, a spherical 

 receptaculum seminis, 132 to 148/z in diameter, and a shell gland in size 

 and form similar to the ovary. The position of these is clearly shown in 

 figure 21. Beginning in the shell gland the uterus immediately upon 



