TRENTON CONGLOMERATE OP RYSEDORPH HILL 75 



SCHMIDTELLA Ulrich 



Schmidtella crassimar^nata Ulrich var. ventrilabiata var. nov. 



Schmidtella crassimarginata Ulrich. Am. geol. 

 1802. 10:269 



PI. 7, fig. 12-18 



Under this varietal designation a form is characterized, which 



is extremely common in the reddish gray, compact, ostracode 



limestone of Rysedorph hill. 



Diagnosis. Carapace broadly suboval, almost equilateral; hinge 

 line nearly straight, shorter than the length of the valye ; cardinal 

 angles obtuse, anterior and posterior margins strongly rounded, 

 the posterior a little more than the anterior one; ventral outline 

 of body of valve uniformly curved. Body of valve very strongly 

 convex, highest dorsally of the center, back of valve projecting 

 above the hinge line, causing the dorsal outline to appear more 

 or less arcuate, and producing an incurving triangular cardinal 

 area. A depressed convex to flat border begins at the cardinal 

 angles and encircles the valve, rapidly widening in the ventral 

 region, and mostly assuming the form of a tongue-shaped or lip- 

 shaped lappet. Surface smooth and shining. 



Dimensions. Length of body of valve of one specimen .7 mm, 

 hight of same .45 mm; thickness .3 mm; width of ventral border 

 .2 mm; length and hight of body of valve of another .9 mm and .6 

 mm and width of border .2 mm. 



Horizon and locality. Reddish gray compact, ostracode lime- 

 stone pebbles of the Rysedorph hill conglomerate. (Group 6) 



Observations. This form agrees in all principal features with 

 Schmidtella' crassimarginata Ulrich, from the 

 Stones river (Lowville limestone) of Mineralpoint Wis., and Dixon 

 111. It differs only in the stronger development, specially in the 

 ventral region, of the marginal border, a difference which can 

 not be considered to indicate more than a regional variety within 

 the confines of the species. 



