BRACHIOPODA. 
Ill 
To Rhynchospira are to be referred, primarily the Lower Helderberg species, 
Waldheimia formosa, W. globosa, and W. rectirostra, Hall. It is also probable that 
the Retzia Electra, Billings, of the Square Lake, Maine, fauna, and the Retzia 
Eugenia, Billings, of the Hamilton group, belong to the same genus. Whether 
the species of the Waverly fauna here described as Rhynchospira scansa, sp. nov., 
is a true Rhynchospira, cannot be determined from the material at hand. 
A very considerable number of species from the American palaeozoic faunas 
have been referred to Retzia, and of several of these it has been impossible to 
obtain representatives for examination Some of the specific names current 
are unquestionably synonyms for earlier terms, but after the elimination from 
the list, of species which may confidently be referred to some of the various 
genera of retzioids here discussed, there will still remain some whose internal 
structure is too imperfectly known to permit a discriminating reference. With 
regard to the so-called Retzias of the British and European Devonian and 
Silurian, it is hardly proper in this place to express more than the opinion 
that farther careful investigation of these shells is necessary to their correct 
generic classification. 
In the development of the fauna of the Niagara group, at Waldron, Indiana, and 
southward, there is a very abundant species, Rhynchospira evax, Hall, 1863, which, 
in specific features, is closely related to the Atrypa aprinis, (de Verneuil) Hall 
{—Retzia apriniformis, Hall, 1859), of the Niagara fauna of New York, and gener- 
ically to the later typical forms of Rhynchospira, though presenting some 
differences worthy of note. The hinge-plate has no posterior extension, 
but its anterior lobes are greatly developed into long, divergent crural bases. 
They are separated to the apex of the beak as in Parazyga hirsuta, and between 
them lies a small linear cardinal process. There is also a stout median septum 
in this valve, whose height is equal to nearly one-half the depth of the valve. 
The loop has a more acute stem and its lateral branches are of the same width 
from their origin to the point of union. It is also frequently the case in this 
species that the deltidial plates remain distinct and uncoalesced at maturity. 
These differences from the typical Rhynchospira are perhaps such as belong to 
an inceptive stage in the development of the genus, but it will serve a good 
