I.AMIII.l I|:K\N< 111 \ I A 



' ' '. i . , ! 



The nmrentrie undiilat ion- ;iU. ;u v more numerous. In a |<. per soon to be puMislir.l 

 I -hall prnpo-e tin- naiii Inntn inn<ln!n for tlii- -mall funn. 



Tlic three species mentioned in the preceding paragraph occupy an isolated 

 position in the genus, and, though they may resemble some of the species of the 

 levata section. I am sati-tie.l tliat they are widely removed from them all. The 

 shape of the anterior ond is peculiar. a- i- also the reticulate surface ornamentation 

 ami the thin liinije plate with its oblique teeth. 



The species under consideration is named for Prof. Samuel Calvin, State Geolo- 



of Iowa. 



formation an<l totality. Maquoketa shales (Hudson River group), at Graf and other localities In 

 Iowa. Also at Scale's Mound In northwestern Illn 



Hut. Keg. No. 8628. 



NODONTA MADIHONEN8I8, n. 8f. 

 PLATE XI.II. ri08. m and M. 



Shell suUov.ite. slightly oblique, moderately convex, 12.5 to 15 mm. in length, 10 

 to 1*2 mm. in liight, and 5.6 to 7 mm. in thickness; anterior end very short, rounded, 



rior margin a little oblique, base broadly rounded and continuing into the 

 anterior margin; dorsal outline slightly concave. Beaks anterior, small, scarcely 

 prominent, incurved; posterior umbonal ridge rounded, inconspicuous; greatest con- 

 vexity of valves in front and above the center. Surface almost smooth, only two* or 

 three obscure lines of growth having been noticed. Test rather thick, hinge strong, 

 posterior denticles geniculated. 



This shell was included in this report and figured under the erroneous impres- 

 sion that it represented a variety of C. calvini. Since the plates were prepared, 

 however, another examination showed differences not before noticed, and when 

 finally the shell was removed from one of the specimens so that a part of the hinge 

 was uncovered, it became fully evident that it was not only distinct but belonged to 

 initi' another group of species. It is namely not fur removed from such species as 

 C. all>t rti/i'i and C. Jilistriata of this report, while it is especially near an unpublished 

 form from the middle beds of the Cincinnati group in Kentucky and Ohio which I 

 shall call C. himida. From these three species C. maduonttuw is distinguished by 

 the more uniform curvature of the anterior margin, the antero-cardinal region in 

 t ho-.- form- being more or less prominent and subangular in outline. 



and locality. -The specimens upon which the specie* Is founded were collected In the 

 Cincinnati group at Madison, Indiana, where they occurred In association with n tHu rttrota. 



