(SASTHOPODA. 



KM III-I..M v 1:1. HVMNI.K.V- /'. (I'lricli. 



1-1 v 1 1 i \\ in. nos. 7-. 



Shell 1') to 20 nun. in diameter, the spire almost flat, the hight between one- 

 thinl aii.l two-seventh- of the width; volutions four, very slightly convex on the 

 upper side, /. . within the outer edge which forms a thin elevated rim; umbilicus 

 very small in casts, apparently dosed in shells. Surface striie fine and subequal on 

 uppe making the usual sigmoid curve, the change incurves occurring near 



tin* mi.l.lU' of the whorU. -hist before reaching the peripheral rim the stria> make 

 another short backward turn. Beneath the periphery the stria* are more unequal. 

 At fir-t they turn forward then more directly inward. 



This species resembles the Chazy If. ralyr Millings, but is smaller and relatively 

 wider. In / of the same author and formation, the edge is blunter, and 



the lines of growth curve more strongly forward beneath it. R. peracutum has an 

 uml.ilicus and diU'ere in several other respects. A very similar species, differing 

 only in that it has a small umbilicus, occurs in the Stones River group in Tennessee. 



Forwuitio* and totality. Hli-hnmml nr. -.Ji>. Kn humml, Indiana. Good speclmena ru 

 CMlM*M.-E.O. 



Genus K.M'HISTOMINA, n. gen. 



(part.) and Plturotomana (part.), of author*. 



Tor generic characters and general remarks see pages 932 and 934 to 939. 



As species of this genus are generally confounded with Raphixtomn, it may be 

 well to repeat the peculiarities upon which we base our separation. In Rdphistniifi 

 the lines of growth on the lower side, which of course correspond with the outline 

 of the lower lip. curve forward more or less strongly from from the peripheral edge. 

 The outer half ami more of the under lip therefore is convex, whereas in i;>ij>/iist<nin<i 

 the corresponding portion is always concave. In species like lt}>hixt<>inin<i Innn-nlina 

 Hillings sp.. this conca\ity i- decided and extends over the whole anterior outline of 

 lower lip. On the upper side of the whorls the stria' curve backward again in 

 Raphistom.i just before reaching the peripheral edge. Thi>. together with the 

 forward nine immediately beneath the edge, produces'a small notch in the outer 

 angle of the aperture. In l{>iphi*tniin>i t on the contrary, there is no notch, tin- 

 angle being either rectangular or turned slightly forward, in some cases forming a 

 beak-like projection. Comparing the upper and lower lips we find that in A'- ////i />/;,/ 

 their outlines do not correspond, the lower being more prominent and -imply convex 

 in the outer two-thirds where the upper forms a sigmoid curve. In J;<ij,1 t i^,m>inn, 

 however, the anterior outlines of the two lips are either equal. <T the lower is more 



