UoUlulodo. I.VMKU.IKKAM IIIATA. 521 



im, Mi|iin|.n|i.i\. . gen. 



<Vr.- ,;irt.) SAFPORO, 1809, Ool. of T.-nn.. M^lMiit mart.), ri.ui. 11, INK, Amr. Ool., 



vil, v. 



Ovate shells of the same general type as ft /* and J/orfiomorpAo, but hav- 

 ing from one to three oblique cardinal teeth in each valve. 



Type: Modiolopai* *NW Ulrich. 



The hinge in thi> ^emi- i> much like that of Ischyrodonta. Ulrich, and I might have 

 placed the species under that genus were it not for the fact that their shells are of 

 the same composition as those of .l/-/W/i.s/v. while the shells of that genus are gen- 

 erally heavier ami of the more calcareous nature characterizing the Cyrtodontid<i . 



The development of distinct cardinal teeth is an important deviation from 

 Modjolopti*, an<! I cannot see how any one could object to the generic separation 

 of ^pecies pn .,!,,;: them. Surely, if Mnd'mmorpha can stand, then M<><H<>l<l<i nni-t, 

 for it-^-laims for recognition are certainly better. This may be seen from the aceom- 







panying sketches of the hinges of the three genera. 



ties of Modiolupuu, Modiomorpka and Modiolodon. a, anterior half of hinge of a 

 rik'ht valve of JJodiolopn* rrrtaillrnrii Mlllrr. from tin- upper part of the Cincinnati group at Versailles, 

 Indiana, b, hinge of a right valve of Modioloptit valuta, a new specie* from n,.- top .,r the Lower 

 Silurian at Waynevllle, Ohio. Thi- -|-. ' *. tlKuinh cloaely related to If. modiolarit, hu a wider hinge 

 plate than In any other specie* of the genus known, c, hinge of a left valve of Hodiomorpha ronerafrfaa 



. I. -]< . from the Hamilton of New York. </, antTior (tart of hinge of riktht valve of HodModon 

 ij-nt'.t i j rt<xi.,nt<i gunti SatTonl:. e and /, of right and loft valves of ModModon trinchtlli (Cyrtodanta 



Hi SaiTi.nl i. and g, of a left valve of Modiolodtm oviformit Ulrich: all from tin- mi.l.r..- Trmton 

 !- 'i '. \V;.- .ii rounty, Tennessee, and from speclnjens kindly given to the author liy 1'rof. 



Saffonl. 



tiolodon yunti ami M. irim-lirlli, two of the most typical species of this genii-. 

 were placed into the genus Cyiiinionla. Hillings, by Prof. S.ill.u I A -Me from their 

 litlerent shell -tnn-ture. they have no right in that genu-. l.ein^ \\ithont postern. r 

 lateral teeth. 



MODIOLODON I-ATI i.rs. n. 



I'l.ATI \\\\!l i 



Shell of medium size, suberect, compressed convex, broad ova 

 lateral: anterior end very -hurt, in the casts occupied almost entirely by the strongly 

 elevated, lohe -like, anterior imj.-nilar srar. Hinge line short, the posterior part of 



