456 Dr. Wallicli on the Ehi'zopods. 



somewhat shorter, and, at all events, less hampered by all round 

 alternatives than those furnished in Prof. Leidy's work, which 

 render his definitions practically useless. I therefore request 

 attention to the subjoined extract from the synoptical list of 

 the Difflugidffi, at p. 240 of the ' Annals ' for March 1864, 

 confining myself, however, to those forms only which bear 

 on the question before us. 



" Genus DiFFLUGiA (Leclerc). 

 " Characters. Animal a testaceous Amoeban. Pseudopodia 

 cylindrical or digitate. Test chitinoid, or chitinoid with 

 additions of mineral matter. 



"Species 1. Dijflugta iDroteiformis. 



" Characters of Test. Form of embryonic test subspherical, 

 from ^ to i of the diameter in one direction being truncated 

 and constituting the aperture. Form of mature test extremely 

 variable. 



" Subspecies 1. Difflugia mitriformis. 



^'^ Characters. Test mitre-shaped, more or less inflated at 

 posterior extremity, and without any fixed ratio between length 

 and breadth. 



" Var. a. D. acuminata. Apex of test acuminate. 



" Var. ^. D. spiralis. Anterior third of test bent back upon 

 its body, so as to present a retort-shape. 



" Var. <y. D. pyriformis. Shape varying from the pear- to 

 the balloon-shape." — Annals, March 1864, p. 240. 



Referring to this arrangement Prof. Leidy has drawn 

 marked attention to my having referred the transitional (or, as 

 I think they may be more correctly termed, the metamorphic) 

 series, described and figured in the ' Annals ' for March 1864, 

 to Diffiugia pyriformis. The following are my reasons for 

 having done so. 



Taking the characters of " Quaclrula symmetrica " in the 

 order in which Prof. Leidy records them, we find this organism 

 described as being " remarkable for the construction of its shell, 

 which is compressed pyriform.^^ Both of these characters are to 

 be found in his definitions given above of Difflugia pyriformis, 

 and also its variety. No. 2, D. compressa. But this is not all. 

 If we turn to plate xxiv. of Prof. Leidy's work, which is 

 devoted to " Nehela " and " Quadrula^ we shall see two 

 tests oi Nelela, figs. 11 and 12, which, without looking at the 

 explanation list, we can at once recognize as constituting an 

 inseparable bond between Nehela and Quadrula on the 

 side of incipient mineral metamorphism, and Nehela and D. 

 pyriformis on the side of outline. In the explanatory remarks 



