STUDIES ON THE DIGENETIC TREMATODES. 419 
not extending much, if at all, beyond the ventral sucker. 
Vesicula seminalis simple; ductus ejaculatorius only shghtly 
convoluted ; distinct pars prostatica; prostatic cells fairly 
numerous. Vagina of no great length. Testes, two, rounded, 
close behind each other, about midway between ventral sucker 
and posterior end of body. Ovary rounded, not far behind 
ventral sucker, and separated from the testes by part of the 
uterus, which is of moderate length, confined between ventral 
sucker and anterior testis. Yolk-glands lateral, extending 
nearly the whole length of the body and uniting behind 
testes. Receptaculum seminis and Laurer’s canal present. 
Ova not very numerous, measuring about ‘075 x ‘04 mm. 
No intra-uterine segmentation. 
Type: St. Laureata (Zeder). Includes also St. trans- 
marina n. sp. [= Crepidostomum laureatum (Zed.) 
Stafford, 1904], and probably two other undescribed American 
forms (see p. 39). 
With regard to the systematic position of the genus it 
probably lies nearer Acrodactyla than Crepidostomum. 
From Bunodera, Patagium, Rhytidodes and others 
it is much further removed. Heymann has already discussed 
the relationship of the genus Crepidostomum to Buno- 
dera and Patagium. ‘The somewhat scanty knowledge of 
the first-named genus did not appear to offer any serious 
obstacle to the inclusion of these three genera under the sub- 
family BunopERIN#, and, in addition, the importance of the 
recognised features of difference was under-estimated, as will 
be evident from what follows. 
The presence of circum-oral swellings or papille being a 
rare and peculiar occurrence amongst Distomids, the most 
natural conclusion is that they must have been evolved from 
some simpler type. That they bear no analogy to the much 
commoner collar of cephalic spines of the Ecuinostomin” and 
other forms has already been amply demonstrated by Looss, 
and needs no further discussion here. The resemblance, 
however, in the internal anatomy of the genera under con- 
sideration, especially of Stephanophiala, to the Axto- 
