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MARTIN 



is subject to tidal exchange. At low tide the pond is approximately fifty 

 by one-hundred twenty feet but, because of the flat terrain, high tide 

 may increase both dimensions by from ten to twenty feet. The pond is 

 rarely disturbed by humans and this accounts, at least in part, for its 

 popularity as a feeding place for many species of shore birds. The feces 

 of these birds assure a rich growth of algae upon which the Cerithidea 

 feed and also supply trematode eggs for the infection of the snails. 



The percentages and types of trematode infections were determined by 

 microscope examinations of the tissues after crushing the snails. Only 

 snails 20 mm or more in length were included in this study. 



OBSERVATIONS 



The number of snails examined per month ranged from 1000 to 1215. 

 In all, 12,995 were studied. The percentages of infected snails varied 

 from 54 to 74 (Fig. 1). 



High percentages of infection were found in December, January and 

 May while the low percentages of the range were recorded for February, 

 June, July and October. The seventeen species of trematodes identified 

 are listed in Table I in order of their frequency of infection. Some infec- 

 tions were too young to be classified and they are listed as unidentified. 

 The peaks and lows of infection by month are also included. 



Species No. c 



Euhaplorchis californiensis 2261 

 small xiphidiocercaria 

 small strlgeid 

 Y-bladder cercaria 

 large xiphidiocercaria 

 large pigmented echinostoms 

 Parastictodora hancocki 

 fin-tailed echinostome 



Parorchis acanthus 

 Catatropis sp. 

 schistosome cercaria 

 Cloacitrema michiganens'is 

 Phocitremoides ovale 

 Cercaria buchanani 

 small opisthorchloidea 



cercaria 

 large strigeid 

 small echinostome 



Unidentified 



8680 



