746 = THE PALEONTOLOGY OF MINNESOTA 
[Platymetopus cucullus. 
Hypostoma transversely elongate, subquadrate, anteriorly convex, posteriorly 
broadly marginate. Central lobe distinctly defined and with two short, lateral, 
trausverse sulci or indentations. 
Formation and locality.—Trenton limestone, Minneapolis; Galena shales, St. Paul; Wykoff, Minn. 
Observations.—This species is quite abundant in the calcareous Galena shales at St. Paul, much 
more so than at the other localities cited. 
There can be no question as to the unity of the parts described above as there is no other species in 
these faunas to which any of them could be referred, and they are moreover closely commingled in the 
fragments of rock studied. 
The species is characterized by the lobation of the head in which it corresponds to the type of 
structure represented by the genus Arges Goldfuss, as interpreted by Schmidt. We accept provisionally 
this subgeneric reference, though it is to be borne in mind that the type of Arges is a Devonian species 
(A. armatus Goldfuss). 
Upon close comparison of our specimens with those described and figured by Schmidt,* I have little 
hesitation in concluding that the two forms are specifically identical. Slight varietal differences may be 
observed in the rather more complete isolation of the lateral glabellar lobes on their posterior margin and 
in the somewhat greater length of the marginal spines of the pygidium in the American specimens. This 
species from the Trenton-Galena, the Arges phlyctenoides Conrad, from the Niagara, a hitherto undescribed 
form from the Lower Helderbergy and the Arges contusus Hall, from the Upper Helderberg, form an 
interesting series in which the subgeneric characters of the cephalon are maintained throughout. Arges 
wesenbergensis is from Schmidt’s étage E, or the Wesenberg zone, associated with Plectambonites sericea 
and Strophomena deltoidea.} 
Subgenus PLATYMETOPUS, (Angelin) Schmidt, 1885 (emend.). 
PiLatymMetToPus cucuLLus Meek and Worthen (sp.), 1865. 
Lichas cucullus MEEK and WoRTHEN, 1865. Proc. Acad. Nat. Sci. Phila., p. 266. 
Lichas cucullus MEEK and WoORTHEN, 1868. Geol. Surv. IIl., vol. iii, p. 299, pl. 1, figs. 6a-e. 
This species which was described from the Trenton horizon of Alexander county, 
Illinois, is characterized by the simplicity of its glabella, there being but a single 
Figs. 66, 67.—Portion of cranidium of Platymetopus cucullus Meek and Worthen, Galena limestone, 
Wykoff, Minnesota. 
pair of furrows, which meet the occipital ring at right angles; and by the slight 
concavity of the median lobe of the glabella on its posterior sone; which gives ita 
* Revision der ostbalt. Silur. Trilobiten, Abth, 2, p. 44, pl. vi, figs. 1—4. 1885. 
+ ARGES CONSANGUINEUS, nom. prapos. This species may be best described as differing from A. wesenbergensis, var. 
paulianus, in the narrower and much less convex frontal lobe, smaller and less elevated lateral lobes, nodiform and not 
Fig. 65.—Cranidium of Arges consanguineus. 
annular third lobes, larger and more elevated ocular nodes, broader and more highly arched occipital ring. The glabella is 
notably less convex, and, taken as a whole, proportionally smaller. The two species average about the same size. 
From the Shaly limestone of the Lower Helderberg group, near Clarksville, N. Y. The type specimens have been 
presented by the writer to the New York State Museum. 
+See Schmidt, On the Silurian Strata of the Baltic Provinces of Russia: Quart. Jour. Geol. Suc., Nov. 1882, p. 522. 
