746 THE PALEONTOLOGY OF MINNESOTA 



[Plntymetopus cucullus. 



Hypostoma transversely elongate, subquadrate, anteriorly convex, posteriorly 

 broadly marginate. Central lobe distinctly defined and with two short, lateral, 

 transverse 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 Helderbergt 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 etage E, or the Wesenberg zone, associated with Plectambonites sericea 

 and Strophomena deltoidea.t 







Subgenus PLATYMETOPUS, (Angelin) Schmidt, 1885 (emend.). , 

 PLATYMETOPUS COCULLUS Meek and Worthen (sp.), 1865. 



Lichas cucullus MEEK and WOKTIIEN, 1865. Proc. Acad. Nat. Sci. Phila., p. 266. 



Lichas cucullus MEEK and WOKTIIEN, 1868. Geol. Surv. 111., vol. iii, p. 299, pi. I, figs. 6a-c. 



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 eucullus 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 slope, which gives it a 



Revision dor intb.il t. BIlur.Trllobltcn, Abtli. 2, p. 44, pi. VI, flgs. 14. 1885. 



t AIUIKK roNSANiiiMNKirs, win. iimim*. This species may lx- best described as ditl'erlnx from A. ii'i-srnlifriirnxi*, var. 

 . In the narrowci and much less convex frontal lobe, . smaller and lc--s elevated lateral lolies. nodlform and not 



Fig. 65. Cranidium of Arges consanguineus. 



annular third lolics. turner and mure elevated ocular nodes, broudor and more highly arched oivlplt.il ring. The glabclla Is 

 notably less convex, and. taken as a whole, proportionally smaller. The t wo specie- a\crau r c almut the same si /.r. 



Knmi the Hhaly limestone of the Lower Helderberg (,'nmp, near Clarksvllle, N. V. The type specimens have been 

 presented by the writer to the New York State Museum. 



*9ee Schmidt, Ou the Silurian Strata of the Baltic Provinces of Russia: Quart. .l..u> i.e., I. -,.. Nov. 1-H'J. p .V.-J. 



