BRYOZOA. 647 



wide. Zocecia in four ranges, with subcircular or ovate aper- 

 ture, 0.12 mm. in the larii'fst diameter, separated by long in- 

 tervals, about three in 0.2^ mm. Peristome very faint, often 

 confluent with the moderately sharp angles of the branches. 



The exceeding delicacy, widely separated zooecial apertures, 

 and quadrangular zoarium of this species, distinguish it from 

 all other species of the genus, excepting N. quadrata, known to 

 me. It is too distinct from that form to require comparisons. 



Position and locality: Associated with the preceding species 

 in the Cincinnati group, Alexander County, Illinois. 



RHOMBOPORA Meek, 1871. 



(Pal. Eastern Nebraska.) 



(Orthopora Hall. Pal. X. Y. Vol. VI, p. XIV.) 

 (For generic diagnosis see page 402.) 



Of the Palaeozoic genera of Bryozoa this genus ranks next 

 in importance to Fenestella and Polvpora, having a known re- 

 presentation in American rocks of no less than 46 species. 

 These range through all the important divisions beginning with 

 the Niagara, where we meet with one species (Trematopora 

 granulifera Hall). In the Lower Helderberg we have three or 

 four, in the Upper Helderberg and Hamilton ten to twelve, in 

 the Lower Carboniferous divisions at least twenty-five, and 

 in the Lower and Upper Coal Measures five. The general charac- 

 ters of the genus are maintained throughout with remarkable 

 persistency, and I cannot mention a single feature, either ex- 

 ternal or internal, in which the Silurian and Devonian species, 

 taken as a whole, differ from the Carboniferous forms. It is, 

 therefore, a little surprising that Hall should propose Ortho- 

 pora for the reception of the majority of the Upper Silurian 

 and Devonian forms, since the ground is fully covered by Rhom- 

 bopora. What is even more astonishing is that Orthopora is 

 defined as a subgenus under Trematopora when the typical 

 species of the two groups are not closely related in any respect, 

 and really belong to different suborders. Even Orthopora as 

 figured in Vol. VI, N. Y. Pal., contains widely divergent forms. 

 Acanthoclema is the name proposed by the same authority for 

 another group of closely related forms. The type species is 



