CRUSTACEA. 
25 
A still more intimate agreement may be found in the form Phacops latifrons, 
var. occAtanus, Tromelin and Grasset, as described by Barrois (Ann. de la Soc, 
Geol. du Nord, vol. xiii, p. 76, 1885), from the lower middle Devonian of the 
Herault. This variety, with all the essential specific characters of Ph. latifrons, 
has the eyes less elevated, the basal glabellar annulation smaller and without 
the strong, central tubercle; the tuberculation of the glabella is finer, and 
the granules on the pleurae of the pygidium less strongly marked. These 
different forms undoubtedly represent the same species in trans-oceanic faunas, 
and are only such variations as might be expected in descendants of the same 
ancestors subjected to different conditions of life. With Phacops fecundus, Bar- 
rande, of the later formations (Hercynian) of the Bohemian Basin, etages F, 
G and H, there is also a close agreement except in the occurrence of sulcate 
annulations upon the pygidial pleurae in the latter species. 
The specimens from the Eureka District and Lone Mountain, Nevada, identi¬ 
fied by Walcott (loc. cit.) as Phacops rana, Green, present points both of similarity 
and difference with the typical forms of the species, at the same time showing 
distinct features allying them to the Upper Helderberg species Phacops cristata. 
They resemble the former species in (a) the absence of spines at the genal 
angles, (b) the apparently simple pleural annulations of the pygidium; they 
are similar to the Upper Helderberg form in (a) the inconspicuous palpebrum, 
(b) the strong palpebral lobe, (c) the deep and broad occipital furrow which 
bears no trace of the transverse ring behind the frontal lobe, (d) the elevated 
and narrow occipital ring, (e) the hypostoma with strong antero-lateral eleva¬ 
tions enclosing shallow depressions, (f) the obtuse and fiattened termination of 
the axis of the pygidium, (g) the interrupted terminal annulations of the axis. 
This western form, as observed by Mr. Walcott, thus appears to be a variety 
connecting the two species named and may eventually be regarded as of distinct 
specific value. 
Distribution. Upper Helderberg group. The occurrence of Phacops rana in 
this formation is not yet established beyond question. A single specimen is 
labelled from the Corniferous limestone near LeRoy, Genesee county. Hamil¬ 
ton group; In the Marcellus shales rarely, at Chapinville, Ontario county : in 
