OF NORTH AMERICA. 
87 
precisely at the point where the road from Santa Fe to Alg-odones crosses the Rio. I have de- 
dicated this fossil to my friend and travelling companion, the celebrated guide and mountaineer 
Antoine Leroux, called by the' Mexicans Don Joachin. 
Explanation of figure. — Plate II , fig. 3. Shell , natural size. 
ISOCARDIA WASHITA n. sp. 
Plate III, %.-2, 2 a, 2 b. 
Description. — Shell orbicular, slightly triangular, length and breadth nearly equal, entirely smooth, sub-equi- 
lateral, gibbous, umbones very depressed, narrow and curved forwards. The cast which I describe is destitute of 
muscular and palleal impressions. 
Observations. — This species resembles extremely the Isocardia neocomiensis of d’Orb. {Paldontologie 
Frangaise , Terrains Crdlaces; tome III, page 45, pi. 250, fig. 9 — 11.) and the Ceromya neocomiensis Agass. 
[Mtmographie des Myes; page 35, tab. 8 f., fig. 11 — 16.); the only difference I have observed being in 
the keel, which is less distinct in the 1 . Washita than in the I. neocomiensis. The European species is 
well known to me, having often found it in the Neocomian of Nozeroy and Censeau, Jura; and also at 
Hauterive near Neuchatel; and I thought at first the Texian species identical with it, and should not be 
at all surprised if a better specimen should show this to be the case. 
Locality. - Rare, in the Cretaceous rocks on the borders of Red river near Preston, Texas. 
Exptanalion of figures. — Plate III, fig. 2. Cast, side view. 
» III, fig. 2 a. Same, buccal side. 
» III , fig. 2 b. Same , umbones side. 
GRYPHAEA SINCATA var. AMERICANA. 
Plate III, fig. 1 (Under the name of Gryphaa sinuala Sow.). 
Description. — Shell sub-orbicular , of gigantic form , one side cuneiform , beak very small laterally incurved and 
partly hidden and covered by the shell. The lower valve is convex, very thick, deep, rounded and ornamented 
with rounded ribs , converging from the edge of the shell towards a centre placed above the beak ; some of these ribs 
are nodulous , slightly undulated and rough. The upper valve is nearly flat. 
Observations. — This species is without doubt the most gigantic Gryphite yet found in North Ame- 
rica; it has the greatest resemblance to Gryphoea sinuata Sow. [Mineral Conchology of Great Britain, table 
336.) of the Neocomian of England, the distinguishing characters do not appear considerable enough to 
make a new species and I regard it as a variety of the above and give it the name of Gryphwa sinu- 
ata var. Americana. The characters distinguishing it from the true G. sinuata, are, that the lower valve 
of the American species is not sub-carinated but largely rounded , and the beak also is less prominent 
and smaller than in the species of the Lower Green Sand of Kent and Yorkshire, England. It is dis- 
tinguished from the Gryphoea aquila Brong. by its form being neither oblong nor so much flattened, and 
from the Gryphwa Couloni Defr. being neither angular nor triangular. 
Beyrich figures under the name of Exogyra Overwegi var. laevigata , tab. 1 , fig. 2 (See : Report on 
the fossils found by Overweg during his journey from Tripoli to Murzuk and from Murzuk to Ghat, by Bey- 
rich, in Monatsberichte iiber die Verhandlungen der Gesellschaft fur Erdkunde zu Berlin -, neueFolge: IX. Band, 
page 154 and following. Berlin, 1852.), a small specimen of Gryphwa, that he considers as a variety 
of the Exogyra Overwegi Leop. de Buch. According to Beyrich it resembles very much the Exogyra 
laeviwscula Roem. from Texas (See: Die Kreidebildungen von Texas, pag. 70 and tab. IX, fig. 3, 3a, 3 b, 
3 c. Bonn, 1852.), and he says they' can hardly be distinguished from each other. If Roemer’s figures 
and descriptions of the E. laeviuscula are exact, there is a great difference in these two oysters and it 
annears to me that this species from the deserts of Fezzan, Africa, is much more nearly related to the 
