38 PLACOCISTA. 



GENUS VI. PLACOCISTA. 



SYN. : Euglypha, Carter. 



Shell compressed oval, hyaline, colorless, with acute 

 border and terminal, elliptical mouth, the border of the 

 latter entire, with acute commissures; plates of the lon- 

 gitudinal alternating rows oval, overlapping, so as to 

 produce hexahedral areas limited by zones of minute 

 ellipses. Lateral borders and fundus furnished with 

 acuminate spines, articulated with the shell. Sarcode as 

 in Euglypha. This genus differ from Euglypha by its 

 entire mouth without dentate scales, and by its articulated 

 spines. 



Placodsta Spinosa. SYN. : Euglypha spinosa, Carter, Archer, 

 Leidy. 



Shell transparent, colorless, compressed oval, with 

 acute, lateral borders, sometimes slightly tapering toward 

 the oral pole ; mouth large, transversely elliptical, with 

 acute commissures and entire, edentulous border ; com- 

 posed of oval, imbricating plates, in alternating longitu- 

 dinal series, the overlapping borders producing hexahe- 

 dral areas limited by zones of minute ellipses ; oral row 

 of plates like the others, and not forming angular teeth 

 as in Euglypha. The lateral, acute border of the shell 

 fringed with movable subulate spines articulated with 

 the shell by a minute knob, usually in pairs, sometimes 

 single and rarely triple. Length, 100// to 136 /JL ; breadth, 

 80// to 96^, and 36// to 60/z ; mouth, 40/* to 60/z ; spines, 

 to 40// long. 



Hob. Moist sphagnum of cedar swamps. 



