492 



HARRY M. MILLER, JR., AND FLORA E. NORTHUP. 



particular host. Before discussing this, the frequence and nature 

 of the infestation with each of the five larvae found will be taken 

 up. Two of them were present only infrequently and in low 

 percentages, and may be dismissed with brief statements. 

 Cercaria dipterocerca sp. nov. was found in only four specimens, 

 three in August, 1924, and one in late July, 1925; and similarly, 

 C. variglandis sp. nov. was found in one host in each of these 



f C. variglandis 

 O C . q uijje tennis 

 x c. dipterocerca 



infestation 

 nith all specie^ 



Auq Sept Oct /vor Dec Jan Fcb Mar Apr Mav June. Julv Aua 



TEXT-FIGURE i. Graphs showing seasonal fluctuation in total infestation of Nassa 

 obsoleta, and infestation with each species of trematode. 



same collections, and once in August, 1925. There is no obvious 

 explanation for the slight and infrequent occurrence of these two 

 trematodes in Nassa obsoleta. It may be that they are normally 

 parasitic in some other mollusk host, but are capable of developing 

 occasionally in this species of Nassa; or the final hosts may be 

 migratory. 



A third species, C. quissetensis sp. nov., was found in eight of 

 the twelve collections, always in very few hosts, and never 

 emerging after isolation of the snail. In the October collection 

 the rediae were filled with mature cercariae; in November and 



