266 



PALJEONTOLOGY OF NEW-YORK. 



which they may be separated from the Swedish specimens. In well preserved specimens from 

 Gothland, the striee are sharp, or round and prominent, and crossed by conspicuous elevated 

 concentric striae, which, towards the margin, are undulated upon the elevations and depressions 

 of the plications. All the New- York specimens I have seen are destitute of the concentric striae, 

 and the longitudinal strite are often flattened. This character, however, may arise from abra- 

 sion or partial exfoliation ; and, in the shale, the presence of iron pyrites, producing solution 

 of the surface by sulphuric acid, is a probable cause of the absence of the more minute surface 

 markings. 



It is not a little interesting to the palaeontologist and zoologist to consider the fact, that 

 while we have no evidence of a plicated surface in this species from the New-York (and pro- 

 bably all American) strata, we yet have another species of similar form, and a similarly striated 

 surface, which is distinctly plicated from beak to base, and never deviates even in the youngest 

 specimens seen. This species (the S. niagarensis) appears to be unknown in Europe, where the 

 other species is common. We can not avoid the thought that the manifestation of a peculiar 

 feature in the S. radiatus of Europe was more strongly developed in a distinct, but allied form, 

 in the western ocean, and which now appears as a characteristic species of the Niagara period. 



Fig. 6 a, h. Ventral and front view of a small specimen. 



Fig. 6 c. A large specimen entirely flattened, which causes the beak to project as shown in the 

 figure. 



Fig. % d. A. specimen from which the shell is partially exfoliated, showing the form of the mus- 

 cular impression. 



Fig. 6 e. Cardinal view of the same, showing the entire extent of the dorsal area and foramen, 

 which is partially closed above, and broadly triangular. This feature is in remarkable 

 contrast to many specimens in the Clinton group as shown on plate 22. 



Fig. 6 /. The interior of a dorsal valve, showing the extension of the plates or laminae on each 

 side of the foramen, with a central one commencing below the beak. 



This character corresponds precisely with the S. niagarensis (see fig. 4 r), where 

 the interior of a small dorsal valve is shown. This coincidence increases the interest 

 in the similar external characters of the two species. 



Position and locality. This species is not common in the shale of the Niagara group, though 

 occurring in many localities in the lower part of the same, associated with the preceding species. 



626. 9. SPIRIFER PYRAMID ALIS (n. 5^.). 



Pl. LIV. Fig. Td-e. 

 Compare Delthyris elevata, Dalman, Vet. Acad. Handl. 1827, pag. 120, t. iii, f. 3. 

 Shell pyramidal ; dorsal valve extremely elevated ; beak acute ; area vertical or slightly bent 

 forwards ; foramen linear, filled by a projecting callosity ; ventral valve semicircular, nearly 

 flat, or convex only along the mesial fold ; surface plicated ; plications subangular, about five 

 on each side of the mesial fold and sinus, crossed by fine threadlike striae. 



