404 MISSISSIPPIAN BRACHIOPODA 



great deposit of shelly matter at the beak and the essential solidification 

 of the rostral portion of the valve; by the broad and deep muscular im- 

 pression ; by the strong plications of the shell ; and by the nearly flat, 

 posteriorly sloping cardinal area. The pedicle valve illustrated by Hall 

 and Clarke, 1 as 8. subcuspidatus is evidently an example of this species. 

 This species differs from S. subcuspidatus in its flatter cardinal area, its 

 longer and transversely concave delthyrial plate, and the solidification 

 of the rostral portion of the pedicle valve. 

 Horizon.- Keokuk limestone. 



Genus PSEUDOSYRINX n. gen. 



Description. Shell essentially like Syringothyris in its outer form and 

 proportions. The pedicle valve with the lateral slopes usually rounding 

 into the cardinal area; internally the dental lamellae are elongate, some- 

 times reaching to or past the middle of the valve, the delthyrial plate 

 well developed, reaching to varying distances towards the cardinal mar- 

 gin of the valve, its free margin describing a concave curve ; no syrinx 

 developed upon its inner surface. The surface of the cardinal area dif- 

 ferentiated into three regions as in Syringothyris, and similarly marked. 

 Punctate shell structure and fine textile surface markings as in Syringo- 

 thyris. 



Remarks. The genus Pseudosyrinx has been established to include a 

 group of spiriferoid shells with high cardinal area, punctate shell struc- 

 ture, and distinct delthyrial plate which differs from that in Syringothyris 

 in the entire absence of a syrinx upon its inner surface. The various 

 species of the genus have commonly been referred to one or another of the 

 species of Syringothyris, but a careful investigation of a large number of 

 specimens has led to the firm conviction that they should be placed 

 in a distinct generic group differing from Spirifer in the main in the same 

 manner as Syringothyris, and differing from Syringothyris in the absence 

 of a syrinx. It was at first supposed that the absence of a syrinx in cer- 

 tain examples of spiriferoid shells with high cardinal area was accidental, 

 but upon the continued occurrence of this feature in specimens preserved 

 in such a way as to show certainly that no syrinx had ever been present, 

 and the association of this condition with other characters of specific 

 value, such as size, proportions of the shell, etc., the conclusion was forced 

 that they should be separated under a new generic name. Besides the 

 absence of the syrinx there are several other features which are more 

 commsonly present in Pseudosyrinx than in Syringothyris; the dental lamellae 

 are commonly continued further anteriorly along the floor of the pedicle 

 valve than in Syringothyris, and the lateral margins of the cardinal area 

 are more commonly marked by a rounding of the surface of the area into 



iPal. N. Y., vol. 8, pt. 2, pi. 26, fig. 11. (1894.) 



