274 



Fig. 200. Pkityostoma lineatn. Side and top 

 views (after Hall ). 



Genus PLATYOSTOMA. roxK.vn. 



[Ety. : Plat i/s,* hro&d; stoma, mouth. ~\ 

 (1842 : Jouru. Acad. Nat. Sci., Vol. YIII., p. 275.) 



Shell with a short, depressed spire, a large, dilated aper- 

 tm-e, and with the inner li]) lying close against the l)ody- 

 whorl. 



Platyostoma LiNEATA. Conrad. (Fig. 200.) (Pal.N, Y., 

 Vol. v.. Pt. IT., p. 21, PI. X.) 



IHstini^-uishing Chiwacters. — Volutions, four or five; large 

 ventricosel tody-whorl, which is regularly convex, and a little 



depressed below the su- 

 ture line; sub-orbicular 

 peristome; thin outer liji, 

 with sharp entire margin ; 

 thickened inner lip, folded 

 and reflexed over the um- 

 bilicus, which in adult 

 specimens is entirely covered ; fine, nearly equidistant, thread- 

 like revolving stride, cancelled by similar concentric strifi'. 



Found in the lower Moscow shale, at Sections 4 and 5 

 (rare) ; in the Encrinal limestone, at Section 5 (common) ; in 

 the Stictopora and Demissa beds, at Section 5 (common, but 

 small); in the lower Trilobite bed, at Section (S (rare); 

 between the Trilobite and Strophalosia beds, in Aveiw's 

 Creek (rather common). 



Platyostoma lineata, var. sinuosa. Hall, has a deep sinus 

 in the peristome, near the umbilicus. 



Found at " Hamburg, on the shore of Lake Erie." (Hall.) 

 Platyostoma lixeata, var. emarginata n. var. (Fig. 

 200A.) (Compare Pal. N. Y., Vol. V., Pt. H., PI. x'., 

 Fig. 7. ) 



Distin^uisliing Characters. — Spire and volutions similar 

 to P. lineata ; body- whorl less ventricose ; the last whorl 



* The correct orthography for this name is Platystoma, but this name was preoccupied 

 for a shell by Klein, in 1753 ; for an insect by Meigen, in 1803 ; and for a fish by Agassiz, in 

 1829. Paul Fisher, in Wi-o, proposed the name Diaphorostonia, in his ''Manuel deConchyli- 

 ologie."" This has been adopted by some authors. 



