I'MhA 

 Don: . ..-I 



OCC1IIKNTAI.K Unit, \ S'i 1 . 

 I-I.ATK I. VII. riO. t. 



Omiiaoenu occidental^ II M i.. i-m. U.-pt. Supt. <io<.l. Sun. Wiscmisln, p. 47. 



Oriifinul tli-srriplion: "Shell elongate, very compressed, extremely expanded 

 Literally. tlu> upper part with curved outline, beyond the middle the edges are more 

 ne.irly parallel; the length (when entire) having been a little less than twice the 

 jroato-t di. mietor. I pper and lower surfaces convex, the one twice as convex as the 

 other. tin- two <lia meters as one to seven; lateral expansions very thin. Septadeeply 

 concave, numerous, closely arranged, twelve to the inch in the central lobe; arching 

 forward- mi the -ido- with a sharp retral . curve a little within the margin, and 

 running backwards in a narrow extension to the edge at a point opposite or below 

 their junction with the siphuncle in the central lobe. Siphuncle oblate [ventral] of 

 medium size where passing through the septa, expanding in the chambers to more 

 than one-half the smaller diameter of the shell, somewhat bilobate from a constric- 

 tion above and below. 



urface apparently smooth, or with only concentric lines of growth." 



The principal characters distinguishing this from the foregoing species will 

 be found in the closer septa of the former and the curvature of the septa on the 

 lateral expansions. The latter feature is not sufficiently emphasized in the quoted 

 description. 



In G. occidentals these saddles are quite regular, the outer and inner slopes 

 together making almost the arc of a circle or the extremital arc of a broad ellipse, 

 hut in G. anceps the saddles do not rise above their height at the junction of the 

 lobes with the body of the shell, whence they are deflected backward in a long, 

 broad curve. The species seem to agree in the general form of the shell and the 

 size of the apical angle. The best preserved specimen fails of agreement with the 

 description in the proportional dimensions of the shell, the minor and major 

 diameter- Kom^ hen- as I to 5, rather than as 1 to 7. The latter ratio would make 

 a much more expanded form than that presented by our specimens. 



ami locality. Oin- rnnii|iT:ililf fr;ttfiii-nt .iml t\\.. ijiiit' imperfect example* are from 

 th.-Tiviit<iti lii .:i.-.-|.-i| l,\ K ii r.ri.ln Tin- nrininal Im-ality i- in t In- . 



UlDSt .if. WlMN.IIMI.. 



