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 Anastkophia 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, f 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 ZT^" 19 



environs of St. Petersburg, has a general external ^^'^ssi&as^' 



resemblance to species of Porambonites, but the fig. isa. 



Tl r-j.1 1 • 1 I'll A cardinal view ol' a specimen of 



cardmal area of the valves is much more highly spiH/er i^Koaungia) TscheffUni. 



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 vai-iation in all these genera in i-egai'd to the ai-tual 

 degree of union in the lamella; of this valve. In Parastrophia they are normally confluent, though P. di- 

 vergent furnishes an exception to the rule in having them free to the bottom of the valve. In Porambonites 

 they appear to be normally discrete. 



t In King's U. S. Geological Explorations Fortieth Parallel, p. 234, pi. i, fig. 16. 1877. 



I Geol. de la Rus.sie, etc., p. 129, iil. ii, ligs. 1, a, h. 



