412 MISSISSIPPIAN BRACHIOPODA 



Genus SPIRIFERELLA Tschernyshew 



Description. Shells large or small, both valves convex, the hinge-line 

 shorter than the greatest width, the cardinal extremities rounded, mesial 

 sinus in the pedicle valve and fold in the brachial valve well developed 

 and without plications, or only slightly plicated, lateral slopes of the 

 valve plicated. The pedicle valve with a moderately high cardinal area 

 whose surface rounds into the lateral slopes of the valve; internally the 

 dental lamellae are very strongly developed and may extend anteriorly 

 beyond the middle of the valve; they are joined posteriorly by a trans- 

 verse delthyrial plate situated a little beneath the level of the general 

 surface of the cardinal area ; the muscular scars situated between the 

 elongate dental lamella? and resembling those of Spirifer. Brachial valve 

 similar to that of Spir.ifer with a slight median septum internally. Shell 

 substance punctate. 



Remarks. These shells have usually been included in the genus Spirifer, 

 although S. plenus has sometimes been referred to Syringothyris. In none 

 of the shells, however, is there any suggestion of a syrinx. They differ 

 from Spirifer not only in the punctate shell structure, but in the exceed- 

 ingly elongate dental lamellae, and are really more closely allied to those 

 shells that have been placed in the new genus Pseudosyrinx in this report 

 than to any other. They differ from this last genus in their much more 

 rotund form, in their much less elevated and more arched cardinal area 

 of the pedicle valve, in their shorter hinge-line and in the more extrava- 

 gant development of the dental lamellae. They seem certainly to be con- 

 generic with the shells described as Spiriferella claim by Douville, 1 al- 

 though there is some doubt as to any of these shells being certainly con- 

 generic with Spiriferella as originally described by Tschernyshew. 2 For 

 the present, however, it seems better to refer them to Spiriferella than to 

 propose a new generic name for them. 



SPIRIFERELLA PLENA (Hall) 

 Plate LX1II, Figs. 5-8 ; Plate LXIV, Figs. 1-4 



1858. Spirifer plenus Hall, Geol. Iowa, vol. 1, pt. 2, p. 603, pi. 13, figs. 



4a-d. 

 1890. Syringothyris f plena Schuchert, 9th Ann. Rep. N. Y. State Geol.. 



p. 37. 



1894. Syringothyris plena Keyes, Mo. Geol. Surv., vol. 5, p. 88, pi. 40, 



%. 8. 



1895. Spirifer plenus Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 37, 



figs. 32, 33. 

 1909. Spirifer plenus Weller, Bull. Geol. Soc. Am., vol. 20, p. 306. 



iBull. Geol. Soc. France, 4th ser., vol. ix, p. 153, pi. 5, figs. 3-5. (1909.) 

 2 Mem. Com. Geol. de St. Petersbourg, vol. 2, No. 2, p. 513. (1902.) 



