414 
THE PALEONTOLOGY OF MINNESOTA. 
[Plectambonites sericea 
“Type: Plectambonites planissima Pander. Lower Silurian of Russia.” (Hall, 
op. cit.,) 
The following American species are referred to this genus: 
Netty tty 
1839. 
1840. 
1842. 
1847. 
1852. 
1856. 
1858. 
1863. 
1873. 
1874. 
1875. 
1875. 
1883. 
1890. 
1892. 
1892. 
1892. 
1892. 
1892. 
. (2?) decipiens Billings, sp., Calciferous. 
. (2?) sordida Billings, sp., Calciferous. 
. sericea Sowerby, sp., Trenton to Clinton. 
. gibbosa W. and S., Middle Galena. 
. plicatella Ulrich, sp., Hudson River. 
glabra Shaler, sp., Anticosti. 
. transversalis Wahlenberg, sp., Clinton and Niagara. 
. transversalis, var. alabamensis Foerste, Clinton. 
. transversalis, var. prolongata Foerste, Clinton. 
PLECTAMBONITES SERICEA Sowerby, sp. 
PLATE XXXII, FIGS. 10-12. 
Leptena sericea SOWERBY. Murchison’s Silurian System, pl]. xrx, figs. 1, 2. 
Strophomena sericea CONRAD. Third Annual Report, Geological Survey of New York, p. 201. 
Strophomena sericea EMMONS. Geology of New York; Report, Third District, p. 47. 
Leptena sericea HALL. Paleontology of New York, vol. i, pp. 110, 287, pl. xxx1B, fig. 2: 
< pl. LXxIx, fig. 3. 
Leptena sericea HALL. Ibidem, vol. ii, p. 59, pl. x x1, fig. 1. 
Leptcena sericea BILLINGS. Canadian Naturalist and Geologist, vol. i, p. 41, fig. 2. 
Lepiena sericea ROGERS. Geology of Pennsylvania, vol. ii, pt. ii, p. 818, fig. 599. 
Lepteena sericea BILLINGS. Geology of Canada, p. 163, fig. 139. 
Lepteena sericea MEEK. Palxontology of Ohio, vol. i, p. 70, pl. Vv, fig. 3. 
Leptena aspera JAMES. Cincinnati Quarterly Journal of Science, vol. i, p. 151. 
Leptena sericea MILLER. Ibidem, vol. ii, p. 57. 
Leptcena sericea? WHITE. U.S. Geological and Geographical Survey west of the 100th Merid- 
jan, vol. iv, p. 70, pl. IV, fig. 7. 
Leptena sericea HALL. Second Annual Report, N. Y. State Geologist, pl. XLVI, figs. 25, 29. 
Leptcena sericea FOERSTE. Proceedings of the Boston Society of Natural History, vol. xxiv, 
p. 293. 
Plectambonites sericea HALL. Palxontology of New York, vol. viii, pt. i, pl. xv, figs. 25-29. 
Lepteena minnesotensis SARDESON. Bulletin of the Minnesota Academy of Natural Sciences, 
vol. iii, p. 329, pl. Iv, figs 24, 25. 
Leptena precosis SARDESON. Ibidem, p. 329, pl. Iv, figs. 26-28. 
Leptena recedens SARDESON. Ibidem, fig. 330, pl. Iv, figs. 29-32. 
Leptceena saxea SARDESON. Ibidem, p. 330, pl. Iv, figs. 33-35 
Description: “Shell small, transverse, semioval, approaching semicircular, con- 
cavo-convex; hinge-line equaling or more frequently a little longer than the breadth 
of the valves at any point farther forward; lateral extremities varying from some- 
what acutely angular to nearly or quite rectangular and not properly reflexed; 
anterior and lateral margins forming together nearly a regular semicircular curve. 
“Dorsal valve concave, its deepest concavity being near the middle; beak not 
distinct from the cardinal margin; area narrow or nearly linear, and ranging at 
right angles to the plane of the valves. Interior showing cardinal margin to be 
minutely [in Minnesota, lower Hudson River specimens, strongly] crenate towards 
the lateral extremities; cardinal process moderately prominent [smooth] and trifid 
[simple, the lateral divisions are portions of the incomplete chilidium or crural 
plates], the middle division being most prominent, with a deep pit at its inner base; 
