\ mnrn.: .ll>. .111-11. 1. rmr. llu< 



-hell it-elf, iiii-1 a flattening of tin- -urface boneatli thoni i- u-ually di-tinpii-l, 

 Anterior niu-ciilar impivs-ion di-tinrt, rciiifdnii, the pair funning ;i strongly i>-lined 

 lobe at the ha-e <if tl ! 'interior srar '. faint. I'.illial line 



rather indistinct. except in the anterior j 



il sub-tance very thi-k in tlie anterior third. l.i;_',imental area with good 

 definition, strongly concave. long, high. luit not wide in a dor.-al \ iew. I'osterior 

 lateral teeth, three in each valve, the upper often much the smallest ; in many cases 

 more nearly hori/.ontal than shown in fig. 1. Cardinal teeth normally three in each 

 valve. sul.eqiial. nearly hori/ontul. slightly rur\ed. Occasionally the upper one is 

 more -lender than u-ual, and one or both of the others divided so that their number 

 may he four or even the in each -Me. 



Tin- -; iich i- one of the most ahundant and best marked fossils of thia 



class found in Minnesota, was at first believed to be identical with I'. I'MCM/OV./W.V Hillings, 

 hut a -ecoii'l comparison with the original description and figure of that spocies 

 seemed to throw some douht upon their identity. This doubt was strengthened to 

 conviction when a few days ago I received from Prof. .Fa- M Sa fiord an authentic 

 iple of Hilling's species. This shows that, despite the close agreement of the 

 ies, Meek and \Vorthen were fully justified in separating their shell. The 

 principal difference lies in the anterior part of the shells, which in I', inconstant is 

 more obtuse than in I and in the upper part just beneath the beaks pre- 



sents a small protuberance where the latter has a lunule-like excavation. This 

 ditlerenre is due to the shape of the anterior extremity of the hinge, this being 

 angular in I'. i'w//i.v/'/>;> ami well rounded in I", ili.i-inrnxis.. 



.pared with other species, I'. i-tnmi<iln Hall. sp.. and \'. suberecia, and V. crasta 

 are all less oblique and of rounder outline; in I M the dorsal outline is 



concave in-tead of con 



- 



'i and locality. Very rnnuiinn in the uppr beds of the Trenton )lmeU>ne at Miaoen; 

 '. Paul; less abundant a i . utti.-r loralttlfs In .uebedi" 



t Jancsvilk-. Illinolt. 



Xtu. Reg. Nos. 202, 320, 070, 3030, 5006, S62S, 5527, 6ff7, 8322, 8930, 8331. 



V \NI-.\K.MI\ m\ ii. 



PL* 



This name is propo-e-l pn>vi>ionally for one or two casts differing from the 

 ordinary form of I". <l'u ntly in one important re-pect only, nan; 



-ulcus and ridge which should traverse the anterior part of the ca-t from the 

 umbones downward is wanting except aliove the anterior nm-cular .scar where a 

 slight flattening of the umbones may represent the sulrus. The beak al-o i- more 

 incurved than in any -p.-cimen of the typical form of rhe species seen. 



