BRYOZOA. 453 



MONOTEYPELLA APPRESSA UMch. 

 PI. XLIV, fig. 1 Id. 



Zoarium consisting generally of very much flattened branches, 

 occasionally sub-cylindrical. Surface smooth, with clusters of 

 cells larger than the ordinary size, little, if any, elevated, three 

 mm. apart measuring from center to center. Apertures of zooecia 

 thin-walled, polygonal, varying in diameter from 0.2 to 0.35 

 mm. In the axial region the walls of the zooecia are very thin, 

 but become thickened in the cortical region. In tangential 

 sections prepared since the plates were printed the median region 

 of the walls exhibit a minutely granular aspect. Zocecial tubes 

 curve but slightly and are still oblique in the peripheral region, 

 though the apertures appear to be direct; about seven of the 

 ordinary zooecia in the space of two mm. Three or four hori- 

 zontal or but slightly curved diaphragms are developed in the 

 transition period of the zocecial tubes. 



M. pulchella Edwards and Haime, from the Wenlock limestone 

 of Dudley, England, has some affinities to this form, but has 

 much larger and more angular zocecia, with comparatively 

 thinner walls; the tabulation also differs. The species here des- 

 cribed approaches more nearly to M. sequalis Ulrich, from the 

 Cincinnati group of Ohio, the type species of the genus, but has 

 thicker walls, a much smaller number of diaphragms that are 

 also differently situated; and the zocecial tubes are oblique in 

 the peripheral region, while in M. sequalis they are direct. 



Position and locality : Hamilton group; Rock Island, Illinois, 

 and Davenport, Iowa. 



PETALOTRYPA Ulrich. 



(For generic diagnosis see page 377.) 



The bifoliate zoarial habit of this genus marks a decided and 

 easily recognized departure from Amplexopora, Monotrypella 

 and Leptotrypa, while in the zocecial features it is about equally 

 related to all of those types. 



