NO. 2 BRACHIOPOD SUPERFAMILY STENOSCISMATACEA GRANT 103 



ABC D 



Fig. 22. — Coledium angarium n. sp., Barnett Shale, Mason Co., Tex.; trans- 

 verse sections XS, USNM 142087, original length 8.9 mm., distances given from 

 pedicle valve beak. 



A. 1.3 mm.: camarophorium wide, cardinal process low. B. 1.8 mm.: cama- 

 rophorium wider. C. 2.0 mm. : dental plates and hinge plate detached from walls. 

 D. 2.2 mm. : hinge plate reduced to thin central part, crura present, intercamaro- 

 phorial plate absent 



The small size and relatively long sharp beak of C. angarium distin- 

 guish it from other weakly costate American species such as C. eruga- 

 tum n. sp. and C. torvum n. sp. Its small size recalls some European 

 species such as C. globulinum (Phillips) (pi. 18, fig. 2) and C. in- 

 dentatum (de Koninck), but its straighter beak and weaker costae 

 distinguish it from them. 



Discussion. — This Mississippian species from the Barnett Forma- 

 tion of Texas is described as a further example (with C. therum 

 (Walcott)) of an early protrusion of the valve edges to form what 

 presages a stolidium. As shown in the illustrations (pi. 12) the in- 

 cipient stolidium of this species is very small, undoubtedly not a struc- 

 ture to function in the same manner as the wide stolidium of Steno- 

 scisma. However, its presence in the Mississippian shows the genetic 



Table 18. — Measurements of Coledium angarium, Barnett Formation, Tex. 



Measurements, in millimeters 



