224: C Schuchert — Brachlopod genus Stjringothyi'is. 



Another phylum originated in the Atlantic realm of the 

 Api)alachian province in Sj>i/'/fer randaUi, which also has a 

 well-developed syrinx, but differs from Si/ringothyris of the 

 Mississippian sea in having a strongly plicated fold and sinus. 

 This stock must be separated generically from those of the 

 Mississippian sea because of its different phyletic derivation, 

 and for it is proposed the generic name Si/rlngopieura (from 

 nyrinx and j!?/<? ?-<?•« or rib, having reference to the plicated fold 

 and sinns), with S. randalli Simpson as the genotyjie. Another 

 species probably also belonging to this stock is Spirifei' alta 

 Hall. Both occur in the basal Mississippic strata of the Appa- 

 lachian province and appear to have no later descendants. 



Another similar development took place during the Upper 

 Devonian (Ouray limestone) in the southwestern Cordilleran 

 sea in Syringosj)ira prima (Kindle, Bull. U. S. Geol. Surv., 

 391, 1909 : 28), a form with an excessively drawn out ventral 

 cardinal area, and valves finely plicate throughout. 



Hall and Clarke mention still other stocks of Spirifer that 

 tend to develop a syrinx. It would therefore appear that any 

 late Devonian or late Mississippian Spirifer with a high cardi- 

 nal area accompanied by much testaceous deposit in the rostral 

 cavity of the ventral valve between the dental plates, may 

 develop a more or less typical syrinx. 



The pedicle in all these forms emerges near the articulating 

 cardinal edge in front of the syrinx and between the slightly 

 diverging deltidial plates. To avoid the lengthening of the 

 inner attached end of the ventral pedicle muscle there was 

 developed the syrinx, a delthyrial plate that was progressively 

 elongated to keep up with the constantly increasing width of 

 the cardinal area. Any independent stock of Spirifer that 

 can be shown to develop a syrinx will have to be distinguished 

 under a distinct generic name to bring out its phylogenetic 

 relations. The establishing of such genera, however, cannot 

 be done without the best of material, and the clear evidence 

 that the various stocks of Spirifer are actually not directly 

 related phylse. In this determination the external characters, 

 as the presence or absence of a plicated fold or sinus, lamellose 

 or spinose growth lines, and the nature of the plications will be 

 of much importance. 



