76 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 51. 



land, England, and Podolia the validity of the establishment of the 

 genus Deltkyiis upon Dalman's species D. elevata will rest upon the 

 proving that that species combines in the same shell the median sep- 

 tum of the pedicle valve with the groove along the middle of the fold 

 of the brachial valve. 



SPIRIFER COBSCOOKI Williams. 



Plate 1, figs. 10, 12, 21, 24. 



1905. Spirifer octocostntus Hall, Williams, U. S. Geol. Surv., Prof. Paper 



No. 35, pp. 22, 23. 

 Cf. Delthyris elevata Dalman. 



A spirifer of the general form of Delthyris elevata Dalman with 

 high area, overarching beak, four plications each side the fold of the 

 brachial valve which is indented by a median groove extending from 

 beak to front. The interior of the pedicle valve has no median 

 septum. 



The original specimens were identified in 1905 with Spirifer octo- 

 costatus Hall,^ by Williams and probably by Shaler, as the name is 

 given in his list of 1886,- though the specimens are not labeled. But 

 they differ from that species both in the absence of a median septum 

 in the pedicle valve and by the presence of the groove along the top 

 of the brachial fold. The species attains a larger size than Spirifer 

 trescotti Williams from the same formation, and the surface mark- 

 ings are similar. The possession of a strongly developed median sep 

 tum, however, distinguishes ^S'. trescotti from this sjDecies. 



The type-specimen of S. cohscooki, represented on plate 1 by figure 

 21, shows a cardinal view in mold of the two valves in conjunction. 

 The dimension of this specimen across the cardinal area is 19 mm., 

 the height from center to center of the two valves at the beaks is 

 14: mm., the width of the delthyrium at the cardinal base 5 mm. 

 Four complete plications are in evidence each side the sinus of the 

 pedicle valve ; where the area meets the outer surface of the pedicle 

 valve the angle is rounded. Another specimen (pi. 1, fig. 10), a 

 mold of the interior of a pedicle valve, shows the sinus to the tip of 

 the beak and v,'ithout trace of the median septum. Still another 

 specimen (pi. 1, fig. 12), a mold of the interior of the brachial valve, 

 shows the groove on the fold extending from beak to front. The 

 surface sculpture consists of fine concentric lamellose lines, fringed at 

 their edges by fine interrupted longitudinal lines. The figure (pi. 

 1, fig. 24) illustrating this character was photographed from a 

 gutta-percha mold of the specimen, which is a mold of the exterior 

 and only imperfectly exhibits the interrupted lines at edges of the 

 concentric lamellae. 



iProf. Paper No. 35, U. S. GeoL Surv., 1895, pp. 22-23. 

 2 Amer. Journ. ScL, ser. 3, vol. 32, p. 58. 



