CRUSTACEA. 
139 
Observations. This species does not widely differ from the ProiHus Macrobivs, 
of Billings, from the Lower Helderberg of Square Lake, Maine. The latter 
species, however, is of considerably larger size, and also differs in the following 
particulars, viz,; the frontal area is not concave; the glabella is longer; the 
axis of the pygidium bears fewer annulations, and the surface of both cephalon 
and pygidium is smooth or minutely punctate. 
This rare species is known in only a few specimens of the cephalon and 
pygidium. One example shows the two parts in juxtaposition, and from this 
fact, and from the analogy of other species of this genus, it is more than 
probable that they belong to the same species and the same individual. 
Distribution. Lower Helderberg group. In the shaly limestone; Near Clarks¬ 
ville, Albany county. 
PhAETHONIDES (?) DENTICULATUS. 
PLATE XXV, FIGS. 14, 15. 
Proetus {Phaiiton) denticulatus, Meek. U. S. Geol. Expl. Fortieth Parallel, part 1, Palffiontolog-y p. 49 ; pi 
i, figs. 10, 10 a, 10 b. 1877. 
Certain fragments, consisting of the pygidium, the glabella and detached 
thoracic segments, were described by Mr. Meek under the above name, and 
though the different parts may not have all belonged to the same species, the 
pygidium, which the author accepted as the type of his description, appears to 
represent a member of the genus Phaethonides. The original specimens have 
not been accessible for examination and comparison, and we therefore repro¬ 
duce the original description of the pygidium, accompanying it with figures 
copied from the work cited; 
“ Pygidium transversely sub-elliptic, and nearly twice as wide as long, with a 
moderate convexity. Its mesial lobe is about as wide anteriorly as each lateral 
lobe (exclusive of their lateral spine-like projections), and more prominent than 
the latter, with three or four segments. The lateral lobes are rather depressed 
and show about four segments each; these segments are not well defined, but 
have each a distinct mesial furrow, extending out to the margin, where each 
segment terminates in a short spine directed backward; while there are two 
other smaller spine-like projections just behind the posterior end of the mesial 
