28 
• PALEONTOLOGY OF NEW YORK. 
DALMANITES, Bareande. 1852. 
HAUSMANNI A, n. s.-g. 
Dalmanites (Hausmannia) pleuroptyx. 
PLATE XI A, FIG, 1-3. 
Asaphus pleuroptyx, Green. Monog. Trilob. North Amer., p. 55. 1832. 
Dalmania pleuroptyx. Hall. Pal. N. Y., vol. iii, ji. 356, iil. 74, figs. 5? 9? (not figs. 1-4, 6-8, 10-12); pi. 75, 
fig. 1 ? 1859. 
This species, tlie most abundant of all the trilobites of the Lower Helder- 
berg faunas, has been found in the Oriskany sandstone of Canada, associated 
with Spirifera arrecta, Streptorhynchus (Orthis) hipparionyx, Phacops cristata and 
Dalmaiiites anchiops, and also in two well-defined examples of the pygidium, in 
the Corniferous limestone of the State of New York. The species thus becomes 
the only member of the trilobitic fauna of the Lower Helderberg known 
to have continued its existence into the Upper Helderberg formations. 
Its occurrence in Devonian horizons affords the opportunity of suggesting 
some corrections of the previous identifications of the species. The two species, 
D. pleuroptyx. Green, and B. micrurus, Green, both of which were established 
upon pygidia, were recognized in the third volume of the Palaeontology of 
New York, and the differences between tliern were there pointed out. It is 
nevertheless true, that while it is not difficult to select examples of such pygidia 
as appear to be specifically distinct, the difierences seem to disappear with 
abundant material, so that upon the basis of the pygidia alone, the attempt to 
separate the two species is exceedingly unsatisfactory. The type specimen of 
D. pleuroptyx was from the Lower Helderberg of the Helderberg mountains, 
and extensive collections subsequently made from this prolific locality show 
that the abundant pygidia of this species are everywhere associated with cephala 
heretofore undescribed, a specimen of which is here figured (pi. xi a, fig. I). 
