620 



W. S. NICKERSON, 



Live as parasites iu pericardiuiii aud renal organs of fresh water 

 Laiiiellibranchs , in intestine of fresh water tishes and in marine 

 Gastropods. 



The species are: 



A. conchicola v. Baer 1827. 

 Iu kidney and pericardium of various species of Unionidae of 

 Europe and N. America, iu Gastropods; also iu immature condition 

 in intestine of Unionidae. 



Ä. limacoides Dies. 1834. 

 In intestiue of diiferent species of Leuciscus in p]urope. 



A. macdonaldi Mont. 1891. 

 In Siphon of Melo in Australia. 



Little is kuown concerning the species A. macdonaldi Mont. It 

 may be considered certain that it is an Aspidobothrid and extremely 

 probable that its nearest affinities are with Aspidogaster. Its internal 

 structure is, however, almost entirely unknown. Externally it diii'ers 

 from all other known Aspidobothrids iu the possession of tentacles 

 (180 iu uumber according to Macdonald) capable of Protrusion and 

 retraction like the tentacles of a snail. It is not improbable that they 

 represent the marginal sense organs of other forms highly modified 

 though they are present not ouly around the margiu of the ventral 

 shield but also in all the iutersections of the ridges which separate 

 the diiferent alveoli. It is possible that a new geniis may have to be 

 created for this species when its internal structure shall become kuown. 



University of Minnesota, Minneapolis, 

 July 10, 1901. 



