830 
PALAEONTOLOGY OF NEW-YORK. 
CRUSTACEA. 
The Crustacea of the Lower Helderberg group are not numerous; and 
though the collections have been continued in the Helderberg mountains, 
and at Schoharie and Carlisle as well as other places, through many years, 
the specimens that have been obtained are for the most part fragmentary. 
The small number of individuals, of nearly all the species, which have 
been found, shows that they are comparatively rare in the localities 
examined. Two species, the Dalmania pleuroptyx and D. micrurus, occur 
in considerable numbers; mostly, however, preserving only the caudal 
extremity. After these, the Pliacops logani; while the Acidaspis tubercula- 
tus is of frequent occurrence in certain layers, but always in the condition 
of fragments. 
The genera occurring in this group are Bronteus, one species; Proetus, 
one species; Homalonotus, one species; Phacops, one species; Dalmania, 
four species; Lichas, two species ; Acidaspis, two species. 
There are, besides the trilobites, several species of Beyrichia and of 
Leperdita. 
Bronteus barrandi (n. s.). 
Plate LXXIII. Fig. 1, 2, 3, 4. 
Pygidium semielliptical; line of articulation straight; rudiment of the 
axis abruptly prominent, nearly twice as wide at its upper edge as the 
length, showing two articulations. Surface around the axis nearly plane, 
and thence sloping more abruptly, and again becoming nearly flat at 
the margin ; marked by seven ribs on each side the median lobe, which 
is wider than the lateral ones and gradually narrowing from the base 
of the axis for one-fifth of its length, below which it gradually expands 
towards the border without bifurcating; its surface scarcely more 
prominent than the lateral ribs, and the furrows limiting it not more 
profound than the adjacent ones : lateral ribs narrow at their origin 
and gradually expanding towards the margin, the upper one wider at 
its outer extremity than either of the others. 
