34 DESCRIPTIONS OF FOUR DISTOMES. 



may well be questioned, as a study of the two species will show. If, however, its 

 excretory vesicle proves to possess a long median stem, the essential identity of its 

 characters, with those of Renifer variabilis, as well as with those of R. ellipticus and 

 R. elongatus, justifies the creation of this new genus to contain them. 



The affinities of Renifer are with the genera Styphlodora and Astia as described 

 by Looss ('99, pp. 592, 590), and forms a connecting link between them. With Astia 

 it agrees in the great length of the median stem of the excretory vesicle and the ex- 

 tent and structure of the yolk-glands. It differs from it in the form and extent of the 

 excretory crura, which are peculiarly formed in Astia and do not extend in front of 

 the acetabulum, in the relative size of the acetabulum, which is smaller than the oral 

 sucker in Astia, in the position of the cirrus-sac, the form of the vesicula seminalis, 

 and the form and position of the testes. Renifer is similar to Styphlodora in the 

 course and extent of the intestine, and in the general disposition of its organs. It 

 differs from Styphlodora in the structure of the excretory vesicle, the position of the 

 testes, the size of the yolk-glands, and the absence of a large receptaculum seminis. 



V. OSTIOLUM FORMOSUM gen. nov., sp. nov. 



Several specimens of this worm were given me some years ago labelled "from the 

 frog." I do not know from what organ they were taken or from what species of frog. 

 It is an elongated, graceful animal (PI. IV, Fig. 6) between 7 millimetres and 10 milli- 

 metres in length, and about 1.5 millimetres in width in the widest region. The 

 thickness averages 0.33 millimetre; the cross-section is elliptical. The outer surface 

 is without spines or scales. The broadest portions of the worm are posterior to the 

 middle. Towards the forward end the body tapers very gradually to the oral sucker; 

 the hinder end is rounded and blunt. The oral sucker is nearly terminal, but 

 slightly subterminal, and measures 0.3 millimetre in width in a large worm. The 

 acetabulum is situated about 2.5 millimetres distant from the anterior end and is 

 distinguished by its small size (PI. IV, Fig. 8). It is only 0.07 millimetre in diam- 

 eter, which is about a twelfth of the width of the worm in this region. It is besides 

 very shallow and its musculature is so weak that it can hardly be a functionally 

 active organ. It is much more likely that it is a rudimentary organ which is in 

 process of retrogression; in fact until I sectioned the worm I supposed I was study- 

 ing a monostomid. 



■ The genital pore is near the anterior end on the ventral surface, a little to the 



