Syw.p.1. of Pl.urwomrtld-.) 



~ul. MI. ''11.111 on the last whorl; -lit about one-fourth volution in length; aperture 

 moderately ol.lique. the edge of the upper lip sweeping backward rather strongly, 

 the lower broadly concave in the middle, the inner lip generally somewhat thickened 

 and reflected. Surface with rather strong lines of growth; on one or both sides of 

 the band often a more or less well-defined smooth space. Type, Bembexia lartcli 

 Munier-Chalmu- -p. 



We lia\e adoptod this name for the group which in America is typified by the 

 well-known Hamilton species, Pl.8ulcomar>jin>it<i Conrad, and includes also PI. plant- 

 it iy. I '1. 'fljiitiir. and PI. nit>-ll<i, described by Hall from the same formation, and 

 ri. ii Meek and Wort ben, and PI. eleijtintulu Hall, two Lower Carboniferous 



shells, the tir.-t from the Keokiik, the second from the St Louis. Excluding the 

 spirally -triated form-, whose relations to the group under consideration we cannot 

 consider as established. />' < VxiV/, as here defined, corresponds very nearly with 

 Koken's " Plfurotomarii int> mipin ." The group, whether viewed as a genus or a 

 snli^enu- i- immaterial, seems to be a perfectly natural one. Provisionally we 

 would give it an intermediate position between the Silurian Eolomaria and the 

 r.irboniferous /;//,-,,,,^,/;-,i, the tendency of variation exhibited by the species 

 being toward the latter, while their general expression reminds one of the former. 

 \. i, De Koninck, 1888. Shell conical or somewhat discoidal, 



umbilicated. Band forming the periphery of the whorls, extremely prominent, 

 thin, flange-like. On the upper side of whorls lines of growth curve backward 

 without interruption from the suture line to the extreme outer edge; on the lower 

 side first forward, then in a broad curve backward, and finally forward again as they 

 turn into the umbilicus. Surface with revolving lines or not Type, PI. limata 

 Lind-trm (/'/. r,, r inntn Sowerby). 



This type of shell is represented in American deposits by Miin-hi^min tcorfhenana, 

 a rather high species described by Miller from the Niagara limestone at Chicago. 

 As now understood the principal peculiarity of Monrlonia, when compared with true 

 PltuntomariUm, lies in the excessive development of the bounding plates of the 

 slit-band. Thi< particular feature reminds one of S^omfkotofttrut, Koemer, and it 

 i- possible that Mourlunin is really allied to that remarkable genus. Still, they are 

 readily distinguished by the sigmoid instead of uniform curve of the lines of growth 

 on the upper side of the whorl- in Enomfkalopttnu. Despite the resemblances we 

 are firmly convinced that the genesis of the two types is quite different. 



\1. K; . "Nu-i -IRA. n. gen. (Ulrich.) Shell almost regularly conical, the base 

 nearly flat, sometimes a little convex but oftener slightly concave; not perforated, 

 though a small umbilical depression is always present; whorls rather numerous, the 

 rir-t three or four, so far as observed, leas flattened on the upper or visible slope than 



