

LARVAL TREMATODES rrom AUSTRALIAN 
FRESHWATER MOLLUSCS, Parr XI 
By T. HARVEY JOHNSTON anp ANNE C, BECKWITH, University oF AvEvaive, 
Fig, 1-16. 
Barwirr papers in this series have been published in the Transactions of the Royal 
Sociely of South. Australia, 1937-1945, The present contribution deals with the 
morphology of the cercaria and metacercarcia, obtained experimentally, of two 
Strigeate trematodes, as yet untecognized as adults. The cercariae were obtained 
from gastropods living in the swamps of the lower Murray River, South Anstralia. 
These are; (1) Cercaria lessoni n. sp., from Planorbis isingi Cotton, Lininaea 
lessoni Deshayes, and Simlimnea subaquatilis Tate; the metacerearial stage 
oceurring in freshwater leeches, Glossiphonia spp.; the adult being probably an 
Apatemon. (2) Cercaria ameriannae n. sp. from Amerianna pectorosa Conrad; 
the metacerearia occuring in tadpoles of Linnodynastes sp. (experimental) and, 
precociously, in Amerianna pectorosa; the unrecognized adult being a Diplostome, 
perhaps a Tylodelphys. 
We desire to acknowledge our indebtedness to Messrs. G. G., F,, B., and 
D. Jaensch of Tailem Bend, L. Ellis of Murray Bridge, and W. MeAnaney 
of Lake Alexandrina, for assisting us in obtaining the moJlusean material; and 
to the Commonwealth Research Grant to the University of Adelaide for financial 
support, Type material has been deposited in the South Australian Museum. 
CrercartA (FURCOCERCARIA) LESSONI n. sp. 
(Fig. 1-11.) 
A small fureocerearia, Cercariu lessoni, has been obtained on a number of 
occasions from three different species of gastropods, Planorbis isingt, Limnaea 
lessoni, and Simlinnea subaquatilis. Eighteen collections of P. isingt from the 
River Murray swamps at Tailem Bend, were made between April, 1937, and 
February, 1941; the snail was not found again until December, 1945, when it 
veappeared in large numbers. Further collections of that species were made in 
January, Mareh and May, 1946, making a total of 3,854 specimens of P. isingi 
collected on all occasions, of which 49 showed infection with C. lessoni, ie. a 
1-2 p.c, infection. The rate of infection in Limnaea lessont, as shown by our 
figures, is a little higher; out of 3,736 snails collected on 43 separate excursions 
between December, 1937, and May, 1948, 112 specimens gave off C. lessoni, i.e, a 
