CRUSTACEA. 
11 
Homalonotus Vanuxemi. 
PLATE V B, FIGS. 1,2. 
Homalonotus Vanuxemi, Hall. Palseontolog'y N. Y., vol. iii, p. 352, j-)!. Ixxiii, figs. 9-14. 1859. 
This species was described from very meager material consisting of detached 
pygidia and a fragment of the thorax. Although it has proven to be a fossil 
of rare occurrence, more complete specimens have since been obtained, which 
make the introduction of the species in this place important both for the pur¬ 
pose of extending the knowledge of its characters and of comparison with the 
Devonian Homalonoti. The very large fragment here figured consists of the 
pygidium and eleven segments of the thorax, the latter part being considerably 
weathered on the left side and over the dorsum. It was obtained from a 
quarry in the Lower Helderberg limestone at Kingston, Ulster county, and 
is so preserved as to retain its normal convexity. This specimen shows that 
the species approximates very closely Homalonotus delphinocephalus, Green, differ¬ 
ing from the latter, however, in the features pointed out in the original descrip¬ 
tion, namely, the greater number of annulations in the pygidium ; the former 
having upon the axis eleven or twelve, including the articulating ring, the latter 
nine or ten; and upon the pleurae the former ten and the latter eight. The 
pleural slopes of H. Vanuxemi appear also to have been considerably broader. 
The cephalon, which is restored in the figure from a fragment (the only example 
yet observed) taken from the limestone at Port Jervis, Orange county, is con¬ 
siderably produced at the anterior extremity, even more than in H. delphinocephalus 
or H. Dekayi. Just in front of the glabella is a gentle and broad depression, 
giving to the frontal prolongation a shovel-shaped surface. The glabella is 
generally smooth, and regularly convex, uidike that of the Niagara species, 
which often shows a lobate character. That the Lower Helderberg species 
attained very considerable size is shown by the restoration of the missing parts 
of the figured specimen, as given upon the plate, indicating that the animal 
reached a length of 275 mm., or eleven inches. 
