360 Jura, Neocomian and (Jhalk of Arkansas. — Marcou. 
American publications I might possess, containing Mesozoic 
Ostracce. I first showed him the "Synopsis of the mollusca 
of the Cretaceous formation," by W. M. Gabb, 1861, unknown 
to him; and then the Second Report of a Geological Recon- 
noissance of Arkansas, by D. D. Owen, 1860, a work entirely 
unknown in France. He saw at once that the Ostreacretacea ? 
Morton, on plates vii and viii, was a new species, and he 
asked me for the formation and locality. But it was impossi- 
ble to answer, because the report does not describe the species ; 
the plates prepared by Owen were found after his death, but 
without text of any sort ; and Mr. E. T. Cox thought best to 
publish them without explanation, From my scanty practi- 
cal knowledge of the geology of Arkansas, I was inclined to 
think that the species must come from somewhere near the 
locality of the Gryhoia pitcherl, in the Kiameshia creek plains, 
and then that it was a Cretaceous species. Coquand said that 
it was different from all the Cretaceous Ostrece that he knew 
of, and asked me to name it. I proposed Ostrea oweni, but 
he preferred Ostrea franklini, on account of Benjamin Frank- 
lin, always popular among Frenchmen. So it came that the 
most characteristic and common of the fossils of the Trinity 
division, or upper Jurassic of Arkansas and Texas was named 
by a foreign palaeontologist, who never came to America, and 
was referred wrongly to the Cretaceous system. 
Professor Hill gives three plates of "figures of every possible 
type of variation,-' plates v, vi and vii, almost all collected at 
the same spot, in a breccia limestone, five feet of thickness, 
composed entirely of these shells, near Murfreesboro, Pike 
county, Arkansas. After a careful study of the plates and of 
a few specimens, I fully believe that Ave have there four distinct 
species. 
On plate v, from figure No. 1 to No. 10, we have a variety of 
the Ostrea virgula. The true and original Exogyra virgula 
Goldfus is a little larger and more hooked or virgulated, if we 
can make use of such a word. I must say that I have seen 
specimens, referred to Ostrea virgula in the Jura mountains 
and in Burgundy, exactly like figures 2, 3 and 7 of Mr. Hill. 
So, on the whole, we can say that we have in the Trinity beda 
of Arkansas, the Exogyra virgula so characteristic of the 
lower part of the Portlandian or Salius marls of central 
Europe. 
