. The Geology of Minnesota . defined over the entire dorsal surface. Formation and locality.—Galana, shales, St. Paul, Cannon Falls; Hudson Kiver group, near SpringValley, Minnesota. Family ASAPHIDtE. • Genus ASAPHUS, Brongniart, 1822. Subgenus ISOTELUS, DeKay, 1824. The original species of Asaphiis, A. expansus Wahlenberg, is of a type which doesnot appear to be represented in the American faunas. Its lobate glabella, distinctlysegmented pygidial axis, and narrow thoracic axis, are sufficiently distinctive togive the term a morphological value when thus restricted. DeKays term Isotelus,very s
. The Geology of Minnesota . defined over the entire dorsal surface. Formation and locality.—Galana, shales, St. Paul, Cannon Falls; Hudson Kiver group, near SpringValley, Minnesota. Family ASAPHIDtE. • Genus ASAPHUS, Brongniart, 1822. Subgenus ISOTELUS, DeKay, 1824. The original species of Asaphiis, A. expansus Wahlenberg, is of a type which doesnot appear to be represented in the American faunas. Its lobate glabella, distinctlysegmented pygidial axis, and narrow thoracic axis, are sufficiently distinctive togive the term a morphological value when thus restricted. DeKays term Isotelus,very significant and proposed two years later, includes species with broad axis andobsolete segmentation at maturity. We therefore believe that an excellent purpose *4th Ann. Rept. Pal. Dept.; N. Y. Geol. Survey, p. 49; cit., p. 28, oast 1. TRILOBITES. 701 Isoteliis gisas— is sabserved in the retention of this name. For purposes of comparison a copy ofDalmans figure of Asaphus expansus is here Fig. 4. Outline of Asaphus expansus Wahlenberg (after Dalman). IsoTELus GiGAS DeKmj, 1824. Isotelus gigas DeKat, 1824. Annals Lyceum Nat. Hist. N. Y., vol. i, p. 174, pi. 12,:Asaphusplatycephalus (Stokes) of most authors. y. 1, pi. 13, flg. 1. Isotelus maximus Locke, 1838. Isotelus maximus Locke, 1838. Second Ann. Kept., Geol. Surv. Ohio, p. 246, flgs. 8, megistns Locke, 1841. Trans. Amer. Assoc. Geol. and Nat. p. 221, pi. megisios (Locke) of most authors. In referring to these two widely known trilobites under the same caption, it isnot the intention to assume their specific identity. It is, however, on many accountsconvenient to consider them together, as careful study of a large series of both formshas elicited some important suggestion concerning their mutual relations. The usual basis of distinction between these contemporaneous fossils is anexceedingly simple one. Constructed upon essentially the same specific type, the one,I. gi
Size: 1291px × 1936px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, bookidgeologyofmin, bookyear1897
