PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 187 
Subclass GASTROCAULIA 
Superfamily DicryoninaAcea Cooper, new superfamily 
Small, transversely elliptical shells having a homoeodeltidium in pedicle valve 
and a broad, open or partially closed notothyrium in the brachial valve. 
Family MICROMITRIDAE Schuchert, 1929 
Conservative corneous brachiopods with delthyrium more or less completely 
closed by a homoeodeltidium. 
The writer places in this family Micromitra, Dictyonina, and Dictyonites. The 
structure of these genera is very similar, and it is no longer possible to assign 
them to the Atremata. They cannot be assigned to the Palaeotremata because 
Thompson defined that order as possessing calcareous shells. 
According to Bell all the genera of the Paterinidae are in need of restudy. He 
feels that some of them are polyphyletic, in which case family reassignments may 
be necessary. 
Dictyonites is unusual because it is essentially a Cambrian type of brachiopod, 
having features that are among the earliest known in the brachiopods. The 
family range is thus extended to the lower part of the Middle Ordovician. 
DICTYONITES Cooper, new genus 
(Greek dictyon, a net) 
Semielliptical in outline ; valves hemiconical in profile, the pedicle valve form- 
ing a fairly high cone; the brachial valve, a low cone; umbonal region of both 
valves smooth and imperforate ; remainder of valves closely perforated by large 
pores to form a fine meshwork (see discussion below). 
Pedicle valve with moderately well formed but narrow pseudointerarea and 
strongly arched homoeodeltidium. Pedicle interior with short median ridge at 
apex. Brachial valve with narrow pseudointerarea and short, arched homo- 
eochilidium. Traces of the musculature not seen in either valve. 
Genotype.—Dictyonites perforata Cooper, new species. 
Discussion.—Many features of this peculiar brachiopod are worthy of discus- 
sion. The general aspect of the shell allies it with the Paterinacea, and the shell 
itself is suggestive of the genus Dictyonina. It is quite unlikely that the shell 
was perforated through its entire substance in life. Two of the specimens indi- 
cate that an impervious outer layer was present, but its true nature cannot be 
ascertained from the material at hand. Evidence points to the possibility that 
the exterior was smooth or marked by concentric undulations. The reticulate 
interior reminds one strongly of the deeply punctate inner shell surface of Jso- 
gramma and Dictyonella. 
Equally intriguing is the development of the umbonal region of both valves. 
This consists of imperforate shell somewhat porcellaneous in appearance form- 
ing a hemiconical apex. From the apex 2 low ridges diverge which separate 3 
depressed areas. The anterior rim of the umbo is slightly protruding and from 
