lO OSBORN. [Vol. XVIII. 



ventral sucker is complex, and it is subdivided into a number of 

 acetabula. The body does not possess the usual oral sucker of 

 the order, but it begins with a pre-oral cavity the "mouth fun- 

 nel," encircled by a very thin and mobile wall, looking obliquely 

 downward and forward and tapering posteriorly to the mouth, 

 which is situated on the summit of a low eminence and opens by 

 means of a narrow vertical slit. The body enlarges as it goes 

 back, till near the posterior end it suddenly becomes bluntly 

 rounded. In Ufe the body is distinctly elevated above the ventral 

 sucker, and its contour is complete posteriorly, but in preserved 

 specimens this distinctness is more or less lost. There is a single 

 excretory opening, located in the middle dorsal line and almost at 

 the extreme posterior end of the body (Fig. 3). The genital 

 organs open by a common orifice, not separately, as stated by 

 Leidy '58. This orifice is in the middle ventral line of the body 

 (Fig. 4) near the level of the front of the ventral sucker. In 

 addition to these openings there are the minute openings of the 

 marginal organs, twentv in number (Fig. 4). The total length 

 of adults taken from preserved specimens varies in 36 cases be- 

 tween 1.2 mm. and 1.8 mm., and the widths of these specimens 

 between 0.6 mm. and i mm. Cotylaspis is thus the smallest 

 member of the family ; Aspidogastcr comes next, 3 mm. X i mm., 

 .while the others are much larger, Cotylogastcr being 10 mm. long, 

 Macraspis 15 mm. long and Stichocotylc 105 mm. long at the 

 maximum. 



The ventral sucker is subdivided by strong ridges bounding 

 deeply concave areas into a very characteristic number of aceta- 

 bula. These are so located that we may recognize a peripheral 

 series of twenty acetabula surrounding a median series of nine 

 (Fig. 4). The two series are further so related that each median 

 acetabulum has one of the peripheral series on each side, and 

 there is one finally at each end of the series. This arrangement 

 is like Cotylogaster michelis, excepting that at the ends in that 

 form there are more than one acetabulum, and it is like Aspido- 

 gastcr except that in it there is a double not a single median row. 

 In Stichocotylc the ventral sucker possesses a single row of 

 acetabula, and Jagerskiold '99 states that Macraspis has a ventral 

 sucker much like that of Stichocotylc. In general, in the Chau- 



