PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 675 
Discussion.—This genus is characterized by its small size, convex valves which 
are smooth or sparsely costated, and the nature of the interior. The pedicle valve 
is provided with strong dental lamellae and fairly large teeth, but the chief generic 
characters appear in the brachial valve. The hinge plate is small and divided, 
each half forming a small triangular socket or crural plate to which the posterior 
ends of the crura are attached. The latter are short lamellae terminating in more 
or less well defined crural processes. The descending lamellae bow outward but 
then curve inward to the jugum which unites them. The spire itself consists of 
a varying part of a single volution. The jugum is a stout band and is generally 
in the form of a more or less pronounced U with the convex base directed pos- 
teriorly and toward the brachial valve. 
The brachidium of this genus is identical with that of immature Zygospira, 
and the genus was put in the synonymy of that common form. Despite the inter- 
nal similarities between the two, the exterior characters of Protozyga are suffi- 
ciently distinct to separate it from Zygospira. Moreover, Protozyga precedes 
Zygospira in its appearance in the geological column and is undoubtedly ancestral 
to it. 
The type specimens of Atrypa exigua Hall on which the name Protozyga is 
based are preserved in the American Museum of Natural History, No. 714/1,2. 
The lot now consists of 5 specimens, but the original lot, to judge by Hall’s 
figures in Paleontology of New York, vol. 1, consisted of 3 specimens. The 
type catalog of the American Museum of Natural History, 1898, lists 4 speci- 
mens only. 
Of the 5 specimens now in the type lot, 1 is a large form, larger than any 
member of the genus hitherto described, and is evidently the specimen referred 
to in Whitfield’s catalog as coming from Watertown, N. Y. This specimen is 
figured in Paleontology of New York, vol. 8, pt. 2, pl. 54, figs. 47, 48, and in the 
Handbook of brachiopods, but it is not figured in the original lot in the Paleon- 
tology of New York, vol. 1. 
A second specimen consists of a small sliver of calcite containing a fairly well 
preserved loop. This specimen is not referred to in the catalog. The 3 remain- 
ing specimens are well-preserved individuals, 2 of which are alike, but the third, 
which is squarer and with other differentiating features, differs quite distinctly 
from the other 2. 
In attempting to select one of these specimens to serve as type for the species 
and incidentally for the genus, too, as the name Protozyga is based on the species 
in question, critical examination of all 5 specimens was undertaken. The calcite 
sliver can be rejected as a possible holotype because it is impossible to link it 
with any external form, and the writer was unable to find a jugum in it. The 
specimen, therefore, does not possess one of the chief defined features of the 
genus Hall and Clarke were describing. The spire enclosed by the calcite seems 
to have the features of the brachidium of Cyclospira. 
The largest specimen which is well preserved would be an ideal type specimen 
if it conformed to the description and if its internal characters could be demon- 
strated. Unfortunately, this specimen is shrouded by difficulties. It measures 
