PALAONTOLOGY. 121 
shell.. This gives the general form satisfactorily, but, for the most part, leaves the external 
markings to be conjectured. The size and form are, however, such, that these alone are suffi- 
cient to distinguish it from other known species, and will enable collectors to recognize it 
wherever it may hereafter be found. 
The rock from which I obtained it is of peculiar an interest, and it is therefore desi- 
rable that its fossils should be as fully made known as possi 
I have placed it in Allorisma with some hesitation, as Prof King, in his definition of the 
genus, describes the position of the posterior adductor muscles as generally much lower than 
they occur in this specimen. In other respects it harmonizes with his description. 
The determination of the generic limits of fossils allied to the one in question seems to have 
given the paleontologists of Europe no little trouble. The genus Alorisma is generally ac- 
cepted by American palontologists, but it is rejected by Morris, who includes the species in 
Myacites, Brown; while Pictet puts them into Pholadomya, Sowerby, and McOoy places them 
in his genus Biaasruenctiees: 
Locality and formation.—The limestone underlying the red and white sandstones, shales, and 
gypsum, at Agua Azul, near the base of Mount Taylor; the equivalent of that exposed at the 
crossing of the Little Colorado, considered by Mr. Marcou as Permian. 
It also contains Productus, Bellerophon, Nautilus, crinoidal columns, &c., and doubtless repre- 
sents the top of the Carboniferous series, though it may here, as do dis equivalent rocks in 
Kansas, include some Permian forms. 
Propuctus Rocerst. Norwood & Pratten. Jour. Acad. Nat. Sci., Philadelphia, vol. IIT, 
p. 9, pl. I, fig. 3. 
The various species of Productus which I obtained from the limestones on the banks of the 
Colorado, at Santa Fé, Pecos, and other parts of New Mexico, probably include most of the 
species obtained by Mr. Marcou from the same region, but I have found it exceedingly difficult 
to establish an identity between my specimens and his figures and descriptions. The speci- 
mens obtained by him, so far as they are represented in his collections deposited in the Smith- 
sonian Institution, do not present the same difficulties of identification with mine, but are 
equally different from his figures. Unfortunately, none of his specimens bear names given to 
them by himself, and the most interesting species to which he refers, as collected by the party 
of Lieutenant Whipple, are not included in his collections in the Smithsonian. 
I have from New Mexico a species of Productus undistinguishable from one in Mr. Marcou’s 
collection procured at the Pecos village, and considered by Prof. Hall, when studying that col- 
lection, identical with P. Rogersi of Norwood & Pratten. Mr. Marcou fails to recognize P. 
Rogersi among those obtained by him in New Mexico; referring all his Producti, with one 
exception, (P. Delawarii,) to European species. Which of his figures are taken from the 
specimens of this shell, what he considers it, or whether he figures it at all, are questions not 
easily answered. 
The figure of what he calls P. scabriculus approaches nearest it in form and markings; nearer 
indeed, it seems to us, than to the true Scabriculus. 
P. Rogersi is characterized by a high and narrow form, ears slightly developed, pit oa 
border less than greatest breadth, &c.; entire surface occupied by fine striations, annular 
folds and tubercles; tubercles most numerous on anterior surface; annular folds obtuse, 
rounded, &c., &c. . 
It has been found in several localities in the Coal measures of Missouri, Illinois, &c. My 
specimens are from Pecos village and from the Coal measures of Kansas. _ 
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