142 FRESH- WATER EHIZOPODS OF NORTH AMERICA. 



the shell, as represented in figs. 24, 29. They probably consist of excre- 

 mentitious matters discharged from the sarcode ball as it assumed the 

 resting condition. Sometimes specimens are met in which the position 

 of the sarcode ball is occupied by a number of pale granular spheres, as 

 represented in fig 25. They are of more uniform size and more definite 

 granular structure than in the spheres of supposed excrementitious matter. 

 Their nature I have not determined, but have suspected them to be spores 

 or reproductive bodies, though they may be entirely foreign to the rhizo- 

 pod. They measure about the ^ th of an inch in diameter. 



I have found no specimens referable to H. elegans which exhibited 

 any clearly transitional disposition toward II. papilio or other forms. 



The thing previously described which appears most to resemble H. 

 elegans is the Difflugia spirigera, of Ehrenberg, from the Bavarian Alps.* 

 If what I have described as series of hemispherical inflections of the shell 

 correspond with his four internal longitudinal spiral lines, the animals are 

 probably the same, though the size he gives is a third less than the smallest 

 of those I have observed. 



QUADRULA. 



Latin, quadrula, a little square. 

 Difflugia: Wallieh, 18(33. AssuUna ; Hologlypha: Ehrenberg, 1871. Quadrula: Schnlze, 1875. 



Shell compressed pyriform, transparent, colorless, composed of thin 

 square plates of chitinoid membrane, arranged in transverse or more or less 

 oblique series, in consecutive or alternating order. Mouth inferior, termi- 

 nal, oval. Sarcode colorless, having the characters of that of Difflugia, etc. 



QUADRULA SYMMETRICA. 



Plate XXIV, figs. 20-25. 



Difflugia proteiforinis, var. symmetrica. Wallieh: An. Mag. Nat. Hist, xii, 1863, 458, pi. x, fig. 16. 

 Difflugia pyriformis, var. symmetrica. Wallieh: An. Mag. Nat. Hist, xii, 1863,467; xiii, 1864, 232, pi. 



xvi, fig. 26. 

 Difflugia symmetrica. Wallieh: Ibidem, 245. 



Difflugia assulata, Ehrenberg: Abh. Ak. Wis. Berlin, 1871,249, Taf. ii, Fig. 4,5. 

 D. AssuUna assulata. Ehrenberg: Ibidem, 240. 

 Difflugia caroUnensis. Ehrenberg: Ibidem, 250, Taf. iii, Fig. 14. 

 D. AssuUna caroliiiensis. Ehrenberg: Ibidem, 246, 274. 

 Difflugia Leptolepis. Ehrenberg: Ibidem, 254, Taf. iii, Fig. 15. 

 D. AssuUna Leptolepis. Ehranberg: Ibidem, 246, 274. 

 Quadrula symmetrica. Schnlze: Areh. mik. Anat. 1875, 329, Taf. xviii, Fig. 1-6. — Leidy: Pr. Ae. Nat. 



So. 1875, 415.— Archer : Quart. Jour. Mic. Sc. 1877, 122. 



"Monatsb. Berl. Ak. Wissens. 1853,526; Abhand. 1871, Taf. iii, Fig. 4. 



