452 MISSISSIPPIAN BRACHIOPODA 



Description. Shell very small, subglobular, ovate in outline, the cardinal 

 extremities not differentiated from the general curvature of the outline, 

 the greatest width near the mid-length, the hinge-line short, about two- 

 fifths the greatest width of the shell. The dimensions of a very perfect 

 specimen of about average size are: length of pedicle valve 5.5 mm., 

 length of brachial valve 4.9 mm., greatest width 5 mm., thickness 3.7 

 mm., length of hinge-line 2 mm. 



Pedicle valve most convex posterior to the middle, the surface curving 

 abruptly from the umbonal region to the postero-lateral margins and 

 becoming a little incurved towards the beak, curving more gently to the 

 antero-lateral and anterior margins; mesial sinus obsolete; beak mod- 

 erately incurved, not coming in contact with the umbo of the opposite 

 valve, perforated by a circular foramen which encroaches upon the 

 umbonal portion of the valve; cardinal area small, concave, with the 

 curvature increasing towards the beak, the inferior, flatter portion lying 

 nearly in the plane of the valve, the lateral margins rather sharply de- 

 fined ; the delthyrium closed by the pseudodeltidium which can scarcely be 

 distinguished from the general surface of the cardinal area. Surface 

 of the valve marked by about sixteen simple, rounded plications, which 

 reach to the beak; they are strongest in the middle of the valve and 

 become fainter towards the cardinal extremities ; the concentric markings 

 faint or obsolete. 



Brachial valve subcircular in outline, about equally convex with the 

 pedicle, the greatest convexity posterior to the middle, the surface 

 curving from the highest point rather abruptly to the cardinal margin, 

 becoming slightly compressed towards the cardinal extremities, the 

 curvature to the antero-lateral and anterior margins more gentle ; on the 

 median line the surface is slightly and narrowly depressed in the umbonal 

 region, the depression being nearly or quite obsolete anterior to the 

 middle : the beak pointed and rather strongly incurved. Surface marked 

 by plications entirely similar to those of the opposite valve and alternating 

 with them, the median plication, however, does not reach the beak but 

 originates in the slight median depression of the valve in the umbonal 

 region; concentric markings like those of the opposite valve. 



Remarks. Material for the investigation of the internal characters of 

 this little shell has not been available, and consequently the generic 

 reference of the species cannot be made with entire certainty. Judging 

 from external characters alone, however, the species has its nearest ally 

 in Hustedia nwrmoni of the Pennsylvanian faunas, the genotype of 

 Hustedia, and because of this the present species is placed in that gemis. 

 This species is smaller than H. mormoni, with relatively finer and less 

 angular plications, and it is proportionally shorter than the average 

 specimens of that species. 



Horizon. Chouteau limestone. 



