28 
APPENDIX. 
ID ONE ARC A. Conrad. 
This genus is limited to Cretaceous strata. The following’ shells are 
exotic species of it : Area Jap>etica , Forbes ; Area disparihs, d’Orbigny ; 
Area Marceana , d’Orbigny ; Ciiculleea glabra, Sowerby ; C. carinata, 
Sowerby ; C. oblonga, Miller. American species — I. Tippana, Conrad. 
LATIARCA. Conrad. 
Differs from the above genus in being without the internal plate. 
L. idonea. Less elevated than L. ononcheila, Roger.-*, with a more de- 
pressed or shorter post-uinbonal slope ; posterior side more cuneiform in 
shape, substance thick ; margin of posterior cicatrix thick, prominent 
acute. Length 3L inches. 
LIOPISTHA. Meek. 
This genus was founded on external characters. Mr. Gabb has published: 
as my opinion that the hinge resembles that of Papyria, but I have no 
recollection of telling him so, nor of having seen the hinge, though I may 
have had a partial view of it. However I have now cleared it from the 
matrix of three valves from Mississippi, and give the following diagnosis : 
Right valve — 2 cardinal teeth just anterior to apex, anterior one short, 
conical, erect, very small, the other oblique, bent or angulated and directed 
anteriorly : left valve— one very small tooth under the apex, triangular or 
pyramidal, erect, flat on top, acute. 
L. protexta , Conrad,. (Cardium.) The ribs are angular and acute, shell 
extremel} 7 thin in substance; the tew ribs on the post-nmbonal slope are 
minutely punctate, and the smooth patt minutely granulated. Casts are 
common in New Jersey, but it is only near Ripley, Mississippi, that the 
shell has been found. 
Cardium subdininen.se, d’Orbigny and C. cornuelianum, d’Orbigny, 
are species of this genus. 
