228 
PALEONTOLOGY OF NEW YORK. 
pedicle-valve, and the convergent plates of the opposite valve which may¬ 
or may not unite before the surface of the valve is reached."^ Again, it has 
been already observed that Anastrophia possesses an uncovered foramen in 
each valve, and this may also be true of Parastrophia, but in Porambonites a 
cardinal area is retained on both valves, and this character, more than any 
other, serves to show the derivation of these shells to be from the same 
ancestral stock as Orthis and its allies. 
In external characters there is also an agreement in contour with the genera 
named. The shells of Porambonites are frequently gibbous, the convexity of 
the brachial valve usually exceeding that of the pedicle-valve. The punctate 
ornament of the exterior lamina is purely superficial. 
While Porambonites is so abundant in the Silurian strata of Russia and Scan¬ 
dinavia, its representation in the American faunas is most meager, if indeed it 
exists here at all. The species Porambonites Ottawaensis, Billings, from the Black 
River limestone, does not belong to this genus, but is probably a member of the 
proposed group Orthorhynchula ; the Porambonites obscurus, Hall and Whitfield, 
described from the lower Silurian of the White Pine District of Nevada,! is 
known only from a single pedicle-valve, which may prove a representative of 
the genus, and, if so, the only one recognized in our faunas. 
The species which was the first of de Verneuil’s 
group of “Spirifer anormaux equirostres,” S.Tscheff- 
kini, de Verneuil,! from the lower Silurian of the 
environs of St. Petersburg, has a general external 
resemblance to species of Porambonites, but the 
cardinal area of the valves is much more highly 
developed and extends for nearly the width of the 
shell. So far as we know, the character of its interior has never been dem- 
* Attention has already been directed to a slight variation in all these genera in regard to the actual 
degree of union in the lamellae of this valve. In Parastrophia they are normally confluent, though P. di- 
vergens furnishes an exce 2 ition to the rule in having them free to the bottom of the valve. In Porambonites 
they ajujear to be normally discrete. 
t In King’s U. S. Geological Exj-dorations Fortieth Parallel, p. 234, jil. i, fig. 16. 1877. 
I Geol. de la Russie, etc., p. 129, jfl. ii, figs. 1, a, h. 
Fig. 159. 
A cardinal view of a specimen of 
Spirifer (Noetlingia) Tscheffkini. 
(De Verneuil.) 
