50 (42) Apertures are sutural openings on the 

 concave umbilical side, plus an open- 

 ing in the final chamber at the end of 

 the umbilical lobe. Diameter 0.35-0.45 

 mm. a, Spiral view; b, umbilical 

 view; c, edge view Tiphotrocha comprimata 



50 (42) Apertures are pores on the face of the final chamber 



.51 



51 (50) Primary aperture is equatorial rather than 

 umbilical. Diameter 0.30-0.35 mm. a. 

 Spiral view; b, umbihcal view; c, edge 

 view Jadammina polystoma 



XlOO 



51 (50) Primary aperture is a slit extending 

 into the apertural face; wall is very 

 finely arenaceous, smooth, glossy. 

 Diameter 0.32-0.35 mm. a. Spiral 

 view; b, umbilical view; c, edge view 

 Arenoparretia mexicana 



X100 



52 (/) Test is pseudochitinous; wall is flexible, collapses when dry; shape is 



ovoid, with an inner and outer collar surrounding the apertural opening. % / Y i n n 



Diameter 0.1 6-0.45 mm Allogromia laticollaris ^- ^ A I 00 



52 (J) Test is calcareous 53 



53 (52) Wall is imperforate and opaque, porcellaneous, usually milky white 54 



53 (52) Wall is perforate and glassy or translucent 68 



54 (53) Coiling is planispiral 55 



54 (S3) Coiling is milioline 56 



19 



