174 APPENDIX E. PALAEONTOLOGY. 



We regret that the specimens of this crinoid from Arkansas are all 

 imperfect, consisting only of detached portions of the cup. It is a 

 fossil peculiar to the western and southwestern States, and eminently 

 characteristic of the superior members of the carboniferous strata, occur- 

 ring in some localities very abundantly. The genus is remarkable, from 

 the fact of its being destitute of a column, in which respect it differs 

 from all known carboniferous crinoids. In young individuals, the di- 

 vision of the pelvis into five pieces is well marked ; but in adult age 

 they are usually firmly anchylosecl, and often all traces of sutures are 

 obliterated. In the centre of the pelvis we observe a small cylindrical 

 tube running nearly its whole length, closed below, but communicating 

 above with the cavity of the cup by a small opening. This structure, 

 probably the nucleus of a column, is only visible when the plates are 

 separated. 



It is associated with the preceding species, in the carboniferous beds 

 of Washington county, Arkansas. 



Pentremites elorealis, Say. 

 Pentremites florealis, Say, 1820, Jour. Acad. Nat. Sciences, IV, 295. 

 Pentatrematites florealis, Roemer, 1852, Monog. Blastoid. p. 33, taf. 

 i. fig. 1 — 4, taf. ii, fig. 8. 



This well-known species is quite common in Washington and Craw- 

 ford counties, Arkansas. The specimens furnished by my brother are 

 rather more globose than those from localities in Kentucky, Indiana, 

 and Illinois. 



Pentremites sttlcattjs, F. Roemer. 

 Pentatrematites sulcatus, F. Roemer, 1852, Monog. Blastoid. p. 34, 

 taf. iii, fig. 10, a — c. — Id. Lethaea Geognostica, taf. iv, fig. 8, a. b. 



We have some doubts as to whether this pentremite is entitled to rank 

 as a distinct species, or whether it should be regarded as merely a 

 variety of P. fl,orealis, which varies considerably in different localities. 

 The form under consideration has generally been referred to P. globosus, 

 Say, by western geologists, from which, however, it is quite different. 

 Mr. Say's description of P. globosus was drawn from a specimen which 

 was brought from Bath, England. 



It is associated with the preceding species in Washington county , 

 Arkansas. 



