28 CENTROPYXIS. 



manner ; mouth circular, entire, surrounded with a row 

 of minute tubercles. Sarcode colored from bright-green 

 chlorophyll corpuscles in the endosarc. Pseudopods digi- 

 tate. Breadth at lateral border, 144/* to 1T6// ; at base, 112// 

 to 136/* ; height, 40/* to GOp. ; mouth, 20// to 28^. Rare. 

 Hob. Ponds. 



GENUS XII. CENTKOPYXIS. 



SYN. : Arcella, Homaochlamys, Ehr. ; Difflugia, Perty ; Centropyxis, 

 Stein ; Echinopyxis, C. and L. 



Shell discoid, circular, oval or ovoid, deepest or thick- 

 est and most obtuse posteriorly, with the base on a level 

 inferiorly and deeply inflected to the mouth, with the 

 dome highest posteriorly, gently curving or sloping for- 

 ward, more abruptly convex backward ; mouth and fun- 

 dus eccentric in opposite directions, the former anterior 

 and inferior, the latter posterior and even, or furnished 

 with a variable number of conical spines. Mouth circu- 

 lar or oval and entire, or with sinuous border, and ex- 

 tending into appendages within, toward the dome. 

 Shell usually brown, but sometimes colorless, composed 

 of chitinoid membrane, mostly incorporated with vari- 

 able proportions of sand, often in such quantity as to 

 resemble Difflugia, never cancellated as in Arcella. 

 Sarcode colorless. Pseudopods digitate. 



aculeata. SYN. : Arcella aculeata, ecornis, Dia- 

 dema, A, centropyxis aculeata, A. Homceochlamys ecornis, A. centropyxis, 

 Diadema, Ehr.; Difflugia aculeata, Perty; Centropyxis aculeata, Stein ; 

 Echinopyxis aculeata, C. and L., Carter, Barnard; Centropyxis, C. ecornis 

 Leidy. 



Form exceedingly variable ; seen from above it usually 

 appears broadly ovoid in outline, with the mouth nearer 



