Cyrtodontaclngulata.] ' LAMELLIBRANCHIAT^A. - 545 



incurved in casts of the interior; in the shell projecting very little above the hinge 

 line. Umbonal ridge very indistinct, with the point of greatest convexity a little 

 above and in front of the middle. In the casts there is a more or less sharply defined 

 and unusually wide depressed or flattened strip running from the beaks downward. 

 Hinge plate wide and strong, with two strong posterior lateral teeth in each valve, 

 and sometimes a third small one above them in the left valve. Anterior teeth con- 

 sisting of one long tooth placed parallel with the margin of the shell in front of ^e 

 beaks and five or six small unequal teeth running downward from the horizontal 

 tooth. Ligamental area well developed. Anterior muscular scar distinct, elongate, 

 vertically disposed, situated immediately beneath the cardinal teeth. Posterior scar 

 illy defined. Shell substance thin, except in the anterior and" dorsal region. 



The small verticailly arranged anterior teeth, and the erect and strongly com- 

 pressed beaks of casts of the interior are the two principal peculiarities of the 

 species. These and other equally obvious characters distinguish it from C. glabella 

 Ulrich. C. saffordi Hall, sp., often has the cardinal teeth broken up in a similar 

 manner, but differs too obviously in other respects to render confusion between 

 them at all likely. 



Formation and looality.— Two opposite valves were collected by Mr. Ohas. Schuchert at Janesville. 

 Wisconsin, in the " Lower Blue limestone." These are now In the museum of the Geological and Natural 

 History Survey of Minnesota. 



Mus. Beg. No. 8324. 



Cyktodonta cingulata Ulrich. 



PLATE XL, FIGS. 7 and 8. 

 Cyprieardites cingulata Uleich, 1892. Nineteenth Ann. Eep., Geol. and Nat. Hist. Suf. Minn., p. 235. 



Shell scarcely reaching the medium size, ventricose in the central and umbonal 

 region, oblique, narrow anteriorly and broadly rounded posteriorly; the outline on 

 the whole, excepting a slight prominence at the postero-cardinal edge, almost regu- 

 larly ovate; hinge line rather short posterior to the beaks, slightly convex. Beaks 

 of good size, strongly incurved, projecting well above the hinge, situated a little 

 more than one-fourth of the entire length behind the anterior extremity; umbones 

 prominent, full, with an obtuse ridge or line of greatest altitude running from the 

 beaks towards the postero-basal side; anterior and cardinal slopes both slightly 

 concave, the latter descending more rapidly. Point of greatest convexity near the 

 middle of a line drawn parallel with and one third of the hight of the shell beneath 

 the hinge. Surface marked with very fine concentric lines, easily abraded, and 

 distant irregular lines or wrinkles of growth. Shell substance thin. Internal char- 

 acters unknown, 



-35 



