OF NORTH AMERICA. 
43 
FOSSILS OF THE JURASSIC ROCKS. 
GRYPHAEA DILATATA var. TUCUMCARII. 
Plate IV , fig. 1 , 1 a , 1 b , 2 , 3. 
DescripCion. — Shell orbicular , distinctly lobed; upper valve flat, circular and cuneiform, lower valve boat shaped, 
sub-hemispherical and elongate. The lateral lobe varies , in some specimens it is very distinct and strongly marked 
in both valves, in others obscure, but it may always be traced. 
Observations. — Many specimens of this species are not distinguishable from the Gryphwa dilatata 
var. (3. Sow. (See: The Mineral Conchology of Great Britain, tab. 149, fig. 2.) 
It differs from the true Gr. dilatata only by its more elongated and less orbicular form, and this 
difference does not appear sufficient to make a new species , more especially as the hinge presents the 
distinction of divergence on the two valves , which is so characteristic of the true G. dilatata of England 
and Normandy. 
In my Rdsumd Explicatif (Tune Carte GMogique des Etats-Vnis et des Provinces Anglaises de TAmO-ique 
du Nord, I say page 883 (See: Bulletin de la Soc. Gdol. de France, vol. XII; Paris, 1855.): «La Gry— 
pluea dilatata var. Tucumcarii n’a aucun rapport avec la Gryphma Pitcherio. 
James Hall, in Observations upon the Cretaceous strata of the United States (See: The American Journal 
of Science, conducted by Silliman and Dana, vol. XXIV; New Haven, 1857.), says page 84: ('Having 
« examined the specimens in ilarcou’s collection, I have no hesitation in saying that the specimens labelled by 
((\t\wi Gryphejea Tucumcarii [— G. dilatata \ nr. Tucumcarii , «Bull. de la Soc. Geol. de France », tome XII, 
« plate 21) are the Gryphcea Pitcheri of Morton, and present no features either in form, character, condition 
« of preservation , or otherwise, which can serve to distinguish them from Gryphwa Pitcherio. 
Here are two clear and decided opinions diametrically opposed to each other. Paleontologists and 
Geologists must decide between them; always bearing in mind that Hall infers from the identity of the 
G. dilatata var. Tucumcarii with the G. Pitcheri , that the rocks of Pyramid Mount « are of unquestionable 
cretaceous age«, and that he mentions neither the Ostrea Marshii, nor the superposition, also regarding 
the Keuper of Pyramid Mount as of unquestionable cretaceous age. 
Locality. — This fossil is very common in the bluffs surrounding Plaza Larga , in the bed of 
Fossil Creek, at the Big and Little Tiicumcari, Pyramid Mount, Monte Revuelto and the Llano 
Estacado. (See: Geological Map of New Mexico, plate VIII.) 
I can say without exaggeration that the members of our expedition have collected three or 
four hundred specimens, and I have seen there myself at least two or three thousand. I met with 
it also near the village of Covero New Mexico, and on the table land or Mesa between Inscrip- 
tion rock and the Canoncito Bonito west of the Sierra Madre. Capt. Pope has found the Gry- 
phata dilatata var. Tucumcarii in the southern part of the Llano Estacado, and Dr. Kennerly gave 
me specimens of that species picked up by him at Leon Spring, between Fort Inge, Texas, and 
El Paso, Chihuahua. 
Explanation of figures. — Plate IV , fig. I . Lower valve of a fullgrown individual. 
» IV, fig. 1 a, 1 b. Upper valve of the same. 
» IV , fig. 2. Young specimen with both valves , showing well the lobe upon 
the upper one. 
» IV , fig. 3. Lower valve of a very long fullgrown specimen. 
OSTREA MARSHII Sow. 
Plate IV , fig. 4. 
Description. — Shell obli(jue , strongly depressed , longer than vv'ide , both valves deeply plaited in six or seven 
angular diverging undulations, edge thick, flatted. 
