. The Geology of Minnesota . n. gen. Cyrtodonta (part.) Safford, 1869, Geol. of Tenn.; Modiolopsis (part.), Ulrich, 1890, Amer. Geol., vol, V. Ovate shells of the same general type as Modiolopsis and Modiomorpha, but hav-ing from one to three oblique cardinal teeth in each valve. Type: Modiolopsis oviformis hinge in this genus is much like that o^ Ischyrodonta, Ulrich, and I might haveplaced the species under that genus were it not for the fact that their shells are ofthe same composition as those of Modiolopsis, while the shells of that genus are gen-erally heavier and of the more
. The Geology of Minnesota . n. gen. Cyrtodonta (part.) Safford, 1869, Geol. of Tenn.; Modiolopsis (part.), Ulrich, 1890, Amer. Geol., vol, V. Ovate shells of the same general type as Modiolopsis and Modiomorpha, but hav-ing from one to three oblique cardinal teeth in each valve. Type: Modiolopsis oviformis hinge in this genus is much like that o^ Ischyrodonta, Ulrich, and I might haveplaced the species under that genus were it not for the fact that their shells are ofthe same composition as those of Modiolopsis, while the shells of that genus are gen-erally heavier and of the more calcareous nature characterizing the Cyrtodontidm. ? The development of distinct cardinal teeth is an important deviation fromModiolopsis, and I cannot see how any one could object to the generic separationof species possessing them. Surely, if Modiomorpha can stand, then Modiolodon must,for its claims for recognition are certainly better. This may be seen from the accom-panying sketches of the hinges of the three Fig. 40. Hinges of Modiolopsis, Modiomorpha and Modiolodon. a, anterior half of hinge of aright valve of Modiolopsis versaillensis Miller, from the upper part of the Cincinnati group at Versailles,Indiana, b, hinge of a right valve of Modiolopsis valida, a new species from the top of the LowerSilurian at Waynesville, Ohio. This species, though closely related to M. modiolaris, has a wider hingeplate than in any other species of the genus known, c, hinge of a left valve of Modiomorpha eoncentrioaConrad, sp., from the Hamilton of New York, d, anterior part of hinge of right valve of Modiolodonganti {Cyrtodonta ganti Safford), e and /, of right and left valves of Modiolodon luinchelli (Cyrtodontawinchelli Safford), and g, of a left valve of Modiolodon oviformis Ulrich; all from the middle Trenton(Orthis beds) of Wilson county, Tennessee, and from specimens kindly given to the author by M. Safford. Modiolodon ganti and M. winchelli, two of the most typica
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