PLATE 4:5. 



Page. 



Figs. 1, o, ft, and 2,c. Corbicdi^4 Moheauensis 534 



l,a. A binge view of right valve (type-specimen). 



J,J». Same view of left valve. 



•2, c. A view of the outside of the last, partly covered by hard, adhering rock. 



I'll.-. V. 11, h. Corbicula Nebrascensis 522 



2, o. Outside of the left valve of the type-specimen. 

 '-'. '>. An inside and hinge view of same. 



Fir. 3. Speuerium recticakdinale 527 



:!, a. A left valve, external view, natural size, of the type-specimen. 

 3,6. An outline dorsal view of same. 



Fig. 4. SiMi.i:i:ir.M fohmosum 526 



4, a. A right-side view, natural size, of the type-specimen. 

 4, 6. Same, magnified. 



4, c. Dorsal view of same. 



Fig. 5. Spn-ERiuM soBELLipficuM 537 



5, a. Left valve, external view, natural size, of the type-speeimeu. 



5, b. Same, magnified. 



Fig. 6. Spblerium planum 526 



6.0. Exterior of a left valve, natural size, of the type-specimen. 



6,6. Profile dorsal view of same. 

 Fig. 7. Corbula mactriformis 528 



7. o. Exterior of left valve, natural size (type-specimen). 



7, b. A dorsal view of same. 



7, c. Au internal and hinge view of same. 



T, (/. Same view of a right valve (type-specimen). 

 7,e. Profile dorsal view of last. 

 7,/. Exterior of right valve. 

 Fig. 8. Unio priscds 516 



8, a. Exterior of a right valve of a young specimen, as traced out by following the lines of 



growth on the umbo of an adult shell. [Bad Lands of Judith River.] 



8, b. Same view of another somewhat different form 1 if same. 

 8,c. Hinge of a right valve. [Judith River.] 



^, rf. Left side of the original type-specimen. [Forty miles up Yellowstone River.] 



En.. 9. Corbicui.a subeluptica 523 



!». o. Exterior of original type-specimen. [Cherry Creek, Dakota.] 



9, h. Hinge and interior of a larger right valve. [Bijou Creek, Colorado.] 

 '.1. c. A magnified view of same. 



Fig. 9 (6i«). Ceritiiiuea I Nebrascensis 559 



9, a (bit). View of the worn type-specimen, with lip broken so as not to show the nature of the 



aperture very clearly. 

 9, b (bis). Au opposite view of same. 



9, c (bis). A magnified view of lower volution and aperture, with the lip broken. 



Fir.. 10. Hydrobia Axtiion vi - r >' 1 



10, a. Showing the natural size of the type-specimen. 



10, b. Same, magnified, so as to give a better view of aperture . 



10, c. An opposite view of same. 



Fig. 11. Hydrobia Warrenana W2 



11, a. A view of the type-specimen, showing its aperture, etc., natural size. 



11, b. Au opposite view, magnified. 



11, e. Same view as 11, o, but magnified. 



