I:U.IUU.\N< IIIA i \ 



l:i>) limy* .Inu.l..] 



This p-nii- i- I'lareil witli much conKdence into the same family as II. ill'* two 

 Devonian genera riinl>i<l*-ll,i aii'l <'itnitti>-i<i and the Carboniferous genus Alloriama, 

 Kinjr. It is with the latter, however, that the implied relationship is easiest eatab- 

 h-hf.l. flu- -i-ncral expression of the shells is not much unlike in the two genera, 

 ami in Imtli the surface i> ^rano-lineate and concentrically plicated; but here we 

 timl one of the [iri-uliarit ie> of the Lower Silurian genus. In the latter, namely, the 

 fol.ls are, when not entirely restricted to the anterior end, at any rate always the 

 strongest there, while in Mlorisina they are strongest in the umbonal and central 

 parts of the valves. The hinge and the muscular impressions also, in the absence of 

 any knowledge to the contrary, are believed to be very nearly the same in the two 

 genera. The principal difference probably is the absence of a lanceolate escutcheon 

 in Itlti/lhuya. \ well defined escutcheon is developed also in Pholadella and ('imi- 

 t'lriu and these genera are further distinguished from liht/timya by their large 

 uin bones. 



In having the concentric surface markings strongest on the anterior end, these 

 -hells agree with Qcdgicickia, McCoy, founded upon Carboniferous species. But after 

 a careful comparison with the figures and descriptions of the species which McCoy 

 himself placed under that genus, I am quite convinced that the Lower Silurian 

 types are not congeneric with the Carboniferous forms. There would be equally 

 good reasons for including them in the same author's genus San</ui<>lHes. 



With the exception of R. sinun/n, which is from the middle Galena of Minnesota 

 and next described, the genus is known only from the rocks of the Cincinnati group. 

 The total number of species known is nine. Of these six are new and three have 

 been described and referred to other genera, namely, S. A. Miller described one under 

 the name of Orthodesma byrnesi, and Whitfield two under the names of Orthodesma 

 mirkleboroughi and Sedgtcickin tuniilnta.* The original of the last species has a well 

 developed lunule and is much shorter than any of the other species. But it is evident 

 that the specimen has been much distorted by pressure. Descriptions and figures of 

 all the Cincinnati species except It. lunnlata are to be published in vol. vii of the 

 reports of the Geological Survey of Ohio. 



KHYTIMYA SINTATA, n. sp. 



I-I.ATT. \\XVI. H09. M an.: 



11 rather small, about -> mm. long, l'_ l mm. hi^li at the beaks, and 11.2 mm. 

 across the posterior enl. with the thickness very nearly equalling the hi^i 

 <linal outline (Ifi-linin^r anterior to the beaks, slightly innate posterior to them: 



A recratriaraloaUoa of RIIMlMC*'orl(lnUrpM of Canadian Lowi-rftllurUn Lniclllbrm-ha pmrw that W* Certain*!* 

 tmma. frnoi the lludw* River nx-k. of ApUcmil. U rralljr apeto of mmHmfU, It to ckeljr rrtatad to R. *** ud 

 1-1 



