SPIRIFER.E OF THE UPPER HELDERBERG GROUP. S03 



This is a fine robust species, of which I have before me a dozen specimens in 

 vai-ious states of preservation, and presenting, in some respects, variations which 

 make me hesitate in referring them all to the same. In some which appear to be 

 well preserved, the area is comparatively narrow, while in others it has a pro- 

 portionally greater width. The plications ajso appear to be of variable strength, 

 and in some of the casts are much stronger than in the shells. In the larger indi- 

 viduals, the general characters are strongly defined, as shown in figures 16, 17 

 and 18, Plate 30 ; while the individual figure 19 was for a long time placed among 

 specimens of S. acuminata, owing to its prominent angular mesial fold, and form 

 of area, which correspond to that species ; but in the curved instead of angular 

 sinus in front, and in the details of the plications, the two are quite distinct. In 

 the more minute surface markings, the concentric striae of 8. acuminata are 

 coarser, and the radiating striaj more frequently interrupted ; but this feature may 

 not prove constant. In its entire form and full pi-oportions it is not likely to be 

 confounded with any other species of the higher formations. 



In some of the casts of this species, we have very nearly the characters repre- 

 sented in the figures of 8. cultrijugata given by Mr. Davidson,* except that the 

 area is not so elevated in the middle. 



Geological formation and localities. This species occurs in the Corniferous or 

 Upper Helderberg limestone at Williamsville and Clarence-hollow, New- York ; 

 and near Columbus, Ohio.f It is unknown to me in the eastern part of the State of 

 New York. 



Spiiifera unica (n. s.). 



PLATE XXX. 



Shell semielliptical ; length and breadth about as seven to ten. Surface 

 finely plicated. 



Ventral valve moderately gibbous, with a broad deep sinus which is 

 undefined at its margins ; umbo prominent, much elevated above the 

 hinge-line, with the beak extremely incurved : outline curving gently 

 from the umbo to the front, and more abruptly to the lateral margins, 

 being concave between the umbo and the cardinal extremities. Area 

 rather low, concave, and scarcely extending to the cardinal angles. 



* Monograph of British Devonian Brachiopoda. Plate viii. 

 t Specimens were obtained from Dr. B. P. Mahh, of Hilford, Ohio. 



