60 
PALEONTOLOGY OF NEW YORK. 
Observations. This name is proposed as a substitute for the term Meristina 
in its current application to species not congeneric with M. Maria. The num¬ 
ber of these species is, probably, comparatively large, and their features subject 
to considerable variation, though, with few exceptions, there are none having 
the structure of the brachidium as described above, which present differ¬ 
ences in other respects sufficient to justify a separation from the type form. 
Heretofore the structure of the loop in this group has not been correctly dem¬ 
onstrated. Mr. Davidson figured and described preparations of Atrypa nitida 
and Terebratula didyma, Dalman* (which he regarded as equivalent terms), 
showing a loop erect and slightly inclined backward at its tip, but without the 
simple posterior prolongation; he applies to these species the generic term 
Meristina. The reasons are given elsewhere for restricting the genus Meristina 
to species similar to M. Maria, Hall; and though the second species mentioned 
in the original description of that genus, Atrypa nitida, agrees rather more 
closely in the form of the loop with the figure given at that time, both 
species vary from the structure as there represented, which is a condition 
not yet known to occur among the brachiopods. It is not unlikely, how¬ 
ever, that this phase of development may be found among some early athyroid 
species. 
We may with reasonable security refer to this genus the following American 
species: Atrypa cylindrica. Hall, A. intermedia, Hall, A. naviformis, Hall, of the 
Clinton group; A. nitida, Hall,f A. crassirostra. Hall ( = A. cylindrica, Hall), of 
the Niagara group, and Charionella? Hyale, Billings, of the Guelph limestone. 
With these are probably to be associated Atrypa ohlata. Hall, of the Medina 
sandstone, and Athyris Harpalyce, Billings, of the Lower-upper Helderberg 
* Silurian Brachiopoda, Supplement, pi. iv, figs. 20-23a. 
t In the original descrijition of this species the appellation nitida was applied to a small form, elongate- 
subtriangular in outline and subtruncate on the anterior margin. At the same time a larger form with a 
more gradual anterior slope was designated as var. ohlata. It is the latter which agrees more closely with 
the very abundant shell in the Niagara fauna of Waldron, Indiana, subsequently identified as Meristella 
nitida (Twenty-eighth Annual Report of the New York State Museum, p. 160. 1879], while the typical 
foi-m of the species is found in the extension of the Niagai'a fauna to the southward, in the vicinity of 
Louisville, Kentucky. The similarity of the Waldron variation to the Meristina didyma, as identified by 
Davidson from the English Silui-ian, is very close, while the typical Atrypa nitida seems to maintain per¬ 
manent differences. The Gotland forms of Atrypa didyma have a higher umbo than any of the American 
shells, constantly exposing the deltidial plates and the entire length of the pedicle-opening. 
