C A in: ON i ri: unr s A c, i: 4! 



of the characters of his i/i-nmun. The ;i]i]):ircnt ahscncc of granules, however, on 

 the- former may !>< due to the condition of the specimen, as tliis is a character easily 

 obliterated by wearing. Of the known foreign species, its nearest represcntathe 

 is perhaps S>ni<jiiiiii>Hi> r<tri<t/,i/is, McCoy (Mrit. 1'al. Ko>s. pi. 8, F, fig. 6-7), from 

 which it differs in bring much narrower posteriorly, and in having a proportionally 

 longer hinge line, particular!) a> coni|)ared with adult specimens of Mc( '\ 's -]><-ci< ^. 

 Its antero-ventral region is ulso more prominent than that of X ntr't.ihilis. 



/."ii/it// mi'/ IH^;I'H,H. Leavenworth City. Kansas; it occurs both in the hills 

 hack of the town, t>(K) to 'J")0 feet above the Missouri, and iu beds of impure 

 limestone near the landing, little above the level of the river. Coal Measures. 

 (Type No. 1011.) 



Sedgwickia '. concnra. 



(PLATE I, Fig. 8, a, 6.) 



Lyoniia roneara, M(KK & HATDKV, Trans. Albany Inst. IV, March 2d, 1858. 



Shell small, rlon?atr-oval ; valves moderately convex in tlie nmbonal and anterior region*. Extremities rounded ; 



r i -n. I . ..ni].r."isl, apparently a littln gaping ; base nearly straight along tin- middle, and rounding up at 



tln> <>\triMiiiti>> ; dorsal outline concave behind the beaks declining iu front. Beaks rather depressed, ini-urv.-.l, 



nii'l located about half-way between the middle and the anterior extremity. Surface of casU with a few more or 



less distinct marks of growth. (Hinge, muscular and pallial Impressions unknown. ) 



Length, O.C5 inch ; height, from base to top of beaks, 0.30 Inch ; convexity, 0.23 inch. 



In first publishing a description of this species, we placed it provisionally in the 

 genus 1. ;/,, iixin, stating, at the same time, that our specimens were merely costs, and 

 that we were consequently left in doubt in regard to its generic relations. Subse- 

 quent examinations of other specimens have satisfied ns, however, that it can 

 scarcely be a Lyonsia there being no impressions in well preserved internal casts, 

 of the projecting cartilage plates so characteristic of that genus. This being the 

 case, we now place it with doubt, in the genus Sedgwickia, to which it api>ears 

 to be more nearly related ; but in so doing, we should remark that until specimens 

 showing the hinge, and other internal characters can be examined, its true affinities 

 cannot be detennined with any degree of confidence. 



Locality ami position. Nebraska, opposite the northern boundary of Missouri. 

 Coal Measures. (Type No. 1023.) 



Sedgwickia? altiroNtrafa. 



(PLATB I, Fig. 9.) 

 Alloritmat altirottrala, MlXK & HATDKX, Proceed. Acad. Nat. Set. Phila. Deo. 1868, 263. 



Shell longitudinally oblong-oval, very gibbons in the nmbonal region ; beaks elevated above the cardinal margin, 

 incurved, and located almost directly over the anterior edge. Posterior side rather broadly and regularly rounded, 

 apparently gaping; anterior side snbtruncate, a little gaping, and rounding into the base below; ventral border 

 nearly straight, or somewhat concave in outline near the middle, and rounding up at the extremities. Cardinal 

 margin straight, rather short. Surface of cast ornamented by concentric undulations, which are small, regular, 

 and well defined on the nmbonal slopes, but become leas distinct, and more irregular near the margins of the valves. 

 Just in front of the most prominent part of the oblique nmbonal ridge of each valve there is a moderately distinct, 

 narrow, undefined sulcns, extending backwards and downwards to the middle of the base. 



Length, about 3.06 Inches; height, from the base to the dorsal margin, 1.57 inch ; do. to the highest part of 

 the beaks, 1.74 inch ; greatest convexity of the two valves, 1.62 inch. 



It is only provisionally we place this species in the genus Sedgwickia, not having 

 seen any specimens showing the hinge ; while the form of the shell is different 



April. 1864. 



