88 MISSISSIPPIAN BRACHIOPGDA 



Brachial valve deeply concave, the greatest concavity near the middle, 

 the concavity becoming shallow in the auricular portions of the valve 

 towards the cardinal extremities ; the cardinal area, the cardinal process 

 and the internal characters of the valve not observed. 



Surface of both valves marked by rather coarse, rounded, radiating 

 costae, separated by intercostal furrows about equal to the costae in width, 

 and increasing by division and intercalation; from two to three costae 

 occupy the space of one millimeter, about 35 being present altogether 

 upon an average sized specimen, upon the auricular portions of the shell 

 they become faint or entirely obsolete. Crossing the costse are fine, 

 raised, concentric markings which are strongly developed upon the tops 

 of the costae and are entirely obsolete in the intercostal furrows, giving 

 to the costae in well preserved specimens a strongly crenulate appearance. 



Remarks. This species was originally described from a single indi- 

 vidual from the Glen Park limestone, which was evidently water-worn 

 before it was fossilized. A comparison of this specimen with numerous 

 individuals from the Chouteau limestone seems to establish the identity 

 of the two forms. In the Glen Park specimen, a pedicle valve, the auric- 

 ular portions of the shell have been eroded and the cardinal extremities 

 seem to be rounded; but the size and convexity of the valve, the costaa, 

 and the nature of the concentric markings are entirely similar in the Glen 

 Park and the Chouteau limestone specimens. The only difference worthy 

 of note is the slightly coarser and consequently less numerous costae on 

 the Glen Park specimen, although some individuals or some parts of indi- 

 viduals from the Chouteau limestone have fully as coarse costae as does 

 the Glen Park specimen. The description here given has been drawn up 

 primarily from the Chouteau limestone specimens. 



The Chouteau limestone specimens included in this species were origin- 

 ally included in the species C. ornatus by Shumard, and the original illus- 

 tration of that species was perhaps taken from one of this species. The 

 description of C. ornatus, however, seems to have been chiefly taken from 

 the Louisiana limestone specimens, and the name is here restricted to the 

 shells from that formation. C. glenparkensis differs from C. ortiatus in 

 the much greater convexity or inflation of the pedicle valve and the 

 greater concavity of the brachial valve, and* in the greater extension of 

 the shell along its hinge-line and consequently in the more conspicuous 

 auriculations of the shell. The ornamentation of the surface, especially 

 the crenulated costae, is similar in the two species, and this character was 

 evidently considered as of specific rank by Shumard, but it is now known 

 to be common to several species of the genus. The species is perhaps 

 most closely allied to C. logani, and has sometimes been so identified, but 

 it may be distinguished by its greater average size, although some ex- 

 amples of C. logani are fully as large as any example of C. glenparkensis, 



