Dr. Wallich on the Rhizopods. 455 



The characters given of Diffiugia pyriformis are : — 

 " Shell pyriform^ flash-shaped or ovoid^ with the narrower 

 pole prolonged into a neck of variable length, of uniform 

 transverse diameters, or more or less compressed] fundus 

 obtusely rounded or subacute, or more or less expanded and 

 variably produced into from one to three conical processes ; 

 neck gradually and evenly narrowed to the oral end, cylin- 

 droid, sometimes constricted; mouth inferior, terminal, circular, 

 or slightly oval. Structure of the shell usually of angular 

 particles of quartz-sand, sometimes mingled with diatoms ; 

 less frequently composed of chitinoid membrane with variable 

 proportions of diatoms and sand. 



" Var. 1. D, pyriformis ; the ordinary characteristic form 

 with the opposite diameters uniform. 



" Yar. 2. D, compressa ; like the preceding, but more or less 

 compressed. 



^' Var. 3. D. nodosa ; usually a large form like the latter, 

 but with the fundus variably produced into from one to 

 three eminences. 



^' Var. 4. D. cornuta ; pyriform, with the fundus provided 

 with one or two pointed conical processes. 



" Var. 5. D, vas ; like the ordinary form, but with the 

 neck defined from the body by a constriction. 



"Difllugia pyriformis is one of the most common species, and 

 it presents much variety of shape and size. The shell is 

 ordinarily flask-like or balloon-form, or, as indicated by the 

 specific name, pear-shaped, with an oval or ovoid body, more 

 or less gradually prolonged into a neck, which tapers to the 

 mouth or is cylindroid, and of variable proportionate length. 



Drfflugia pyriformis by gradual transition merges 



into D. glohulosa^ D, acuminata, &c." — Op. cit. pp. 99 to 

 105. 



For reasons stated at great length by the author (pp. 99 to 

 105) , but which are nevertheless far from being clear, Difllugia 

 proteiformis is altogether excluded from his list of estab- 

 lished species. At p. 113 he says : — " The name D, protei- 

 formis is exceedingly indefinite in its application." And 

 further on the characters of D. proteiformis are again cur- 

 sorily referred to and followed by the remark that " Dr. 

 Wallich uses the name of D. proteiformis in a sort of generic 

 sense, and regards all other forms of the genus ordinarily 

 recognized as transitional subspecies and varieties." 



With reference to the last remark I can only say, in all 

 good faith, " I own the soft impeachment," and, notwith- 

 standing the inference it involves, I prefer still to adhere to 

 my own definitions given below, as being more to the point, 



