228 BULLETIlsr 7*7, UNITED STATES NATIOlSrAL MUSEUM. 



American and European forms, have characters in common which 

 fully justify the recognition of a distinct genus. Although Dianu- 

 lites could not hitherto be regarded as a valid genus, the name is still 

 available, and I propose to retain it with the characters presented 

 by the genotype D. fastigiatus. 



Generic diagnosis. — Zoarium massive, elongate, bluntly turbinate 

 in the type species, solid and hemispheric in other forms; ba.sal surface 

 covered with an epitheca. As in most other monticuliporoids, 

 maculae are present, either as groups of larger cells opening on a plane 

 with the other zocecia, or as clusters of both large and small zooecia 

 arising into monticules. Zooecia polygonal, thin-walled, separated 

 by numerous mesopores as in the type species, or with mesopores few 

 and, in some cases, practically absent. Acanthopores absent but 

 numerous small granules may be observed on the zooecial walls at the 

 surface and in thm tangential sections cutting the oldest part of the 

 peripheral region. Walls of zooecia amalgamated and showing little 

 structure beyond the granules just mentioned. In fractures the zooe- 

 cial tubes break unevenly across or through the walls instead of part- 

 ing between them as in most associated Trepostomata. This style 

 of rough fracture results in a vitreous or crystalline appearance which 

 has been found most characteristic of this and related genera. Dia- 

 phragms always present but varying in number in the different 

 species. 



Genotype. — Dianulites fastigiatus Eichwald. Middle Ordovician of 

 Russia and Sweden. 



Thin sections show a minute structure of the walls that is unlike 

 all other bryozoan genera save NicJiolsonella. In vertical sections 

 the otherwise structureless walls sometimes present an obscure 

 lineation arranged vertically. Tangential sections show this lineation 

 to be due to mmute column-like granulose structures composed of 

 darker calcite. In such a section, a wall with the structure well 

 preserved will, therefore, be made up of alternating light and dark 

 spots. This appearance has been observed in an American species, 

 Monotrypa {? CJiaetetes) cumulata, from the Trenton group of Minne- 

 sota. Ulrich noted its peculiarity of structure, but believed that it 

 might be due to secondary causes, and therefore hesitated in referring 

 the species to Ohaetetes, with which genus the column-like structure 

 in the waUs seemed to ally it. With only a single species at hand, 

 this hesitancy on his part was only natural, but with numerous exam- 

 ples of the four species here described in addition, and also their great 

 differences in geologic and geographic occurrence, I am convinced that 

 the peculiarities are structural and not due to preservation. Con- 

 cerning the relation of Dianulites to Ohaetetes, 1 am at present unable 

 to discuss the subject further than to express the opinion that careful 

 work on the latter genus will show it to be distinct, although possibly 

 allied to the former. 



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