342 



ERNEST CARROLL FAUST. 



through a single pore (Fig. 3). In the parthenita, then, as well 

 as in the cercaria, the basis of the system is a two-fold one, as 

 expressed in the formula a + a" '. 



While many monostome cercaria have been described and in 

 most cases the tubular circuit has been figured in the description, 

 the lateral system or secondary tubule has been suggested only 

 once, in Cercaria robusta (Faust, 1918). Omission of the more 

 delicate part of the system is undoubtedly due to the ease with 

 which the main mass of the system has been observed, since it 

 is filled with granules, and the extreme difficulty with which 



FIG. 3. Very young redia of C. spatula, showing digestive tract and flame-cell 

 structure. X 75- 



the finer tubules are demonstrated. Since this same type of 

 system is probably common to these two species, the formula 

 a + a" is quite likely a common denominator for the family or 

 subfamily to which they belong. 



Cercaria spatula nov. spec. (Figs. 1-3.) 



Systematic position: larval monostome, probably Notocoty- 



lidae. 



Parthenita: redia. 

 Host: Physa gyrina Say. 



