202 Henry LesLıE OsBorN, 
a) Introduction. 
The genus Cotylaspis was founded by Leıpy (1857) for the 
reception of a trematode found in the Unionidae of the Schulykill 
River. His account deals merely with taxonomic features. POIRIER 
(1884) described a form now known to be closely allied, from Tetra- 
thyra, a chelonian from the Senegal river in Africa, designating it 
Aspidogaster lenoiri. His account does not give minute structural 
details to any extent. MonricezLt (1892) in revising the Aspido- 
bothridae instituted the genus Platyaspis for Porrrer’s species. The 
present writer (1898) found Cotylaspis insignis in Lake Chautauqua 
and erroneously referred it to Platyaspis from its resemblance to the 
African animal and through ignorance of the genus Cotylaspis. 
Koroip (1899) corrected this error and showed the identity of my 
species with that of Leıpy, retaining the genus Platyaspis, instituted 
by Monticenu1 for the African form. Nickerson (1902) discarded 
the genus Platyaspis on account of its extremely close relation with 
Cotylaspis and placed Porrrer’s form with C. insignis as C. lenoiri. 
I accept Nickerson’s reasons for this as valid and shall refer to 
the African species in this paper as C. lenoiri. The Aspidobothridae 
is a family of great interest to students of trematode morphology 
so that an account of the structure of one of its hitherto little 
known members is justifiable. We are already well acquainted with 
the structure of Aspidogaster, thanks to HuxLEY, VOELTZKOW and 
STAFFORD, with Séichocotyle (juv.) through Nickerson, and with 
Cotylogaster through MONTIcELLI and Nickerson. Of Macraspis very 
little is on record. 
My material was obtained at Lake Chautauqua, New York, 
where unfortunately it was possible for me to be located only in 
July and early August, and not through the year, rendering it 
impossible to have material for study at all seasons. C. insignis is 
small enough to study alive under compression and most of the 
points have been recognized in this way. Compressed specimens 
killed (HgCl,) and mounted whole after staining in borax carmine 
are very servicible for the general anatomy. Material for 
sectioning was killed and fixed in various reagents: HERMANN’S, 
FLEMMING’s and PERENYTS fluids, Mayer’s picro-nitric, and saturated 
aqueous solution of corrosive sublimate were tried. The corrosive 
sublimate followed by iron-haematoxylin staining was found in 
general the most effective. Methylene-blue intra vitam, was tried 
