532 



GEOLOGY. 



Fig. 238. — The Genevieve (Upper Mississippian) Fauna. Crinoidea: a, Agassizo- 

 crinus dactyliformis Shum., one of the inadunate crinoids which has lost its stem 

 and become a free swimming creature, at least in its adult condition; b, Acro- 

 crinus amphora, W. and Sp., a peculiarly specialized camerate crinoid with a large 

 number of supplementary plates introduced between the basal and radials. It 

 has but two basal plates, not shown in the figure. This genus occurs in the Genevieve 

 and in the Carboniferous, being the only genus of camerate crinoids crossing this 



■ line; c, Pterotocrinus bifurcatus Weth. This genus is restricted to the Genevieve 

 faunas. It is a camerate crinoid with two basals, and possesses five remarkable 

 spines developed from the ventral surface and produced beyond the arms. Blas- 

 toidea: d, Pentremites robustus Lyon. Many species of this genus are known in 

 the Genevieve faunas, some species being represented by innumerable individuals. 

 Cephalopoda: e, Orthoceras annulato-costatum M. and W., one of the more ancient 

 straight, cephalopods, occasional species of which persisted to the close of the 



..,_ Paleozoic; /, Goniatites kentuckiensis S. A. M., a notable feature of the Genevieve 

 * 'fatiiias is the recurrence of the goniatites after their absence from the Osage faunas. 



■ -Brachiopoda: g, Productus marginicinctus Prout, and h, Productus fasciculatus 

 McCh., two of the numerous species of this genus which constitutes a conspicu- 

 ous element in the Genevieve fauna; i, Martinia glabra M. and W., one of the 

 brachiopods having much closer relatives in the Devonian than in the Osage faunas; 

 "7, Spirifer increbescens Hall, one of the most characteristic species of the later 

 Genevieve faunas; k, Spiriferina spinosa (N. and P.), a representative of a genus 

 which was an outgrowth from Spirifer, and has its greatest development in the 

 Genevieve and Carboniferous faunas. It is characterized by its punctate shell 

 structure, J , Seminula subquadrata (Hall), a species which has no near ally in 

 the earlier faunas, but is closely related to later Carboniferous species; w, Eumetria 

 marcyi (Shum.), a representative of a genus which is abundant in the Genevieve 

 faunas and which was also present in the Kinderhook, but absent from the Osage 



'''faunas until near the close of that epoch; n, Leiorhynchus quadricostatum (Van.), 

 Q j; •;•& species common in some portions of the eastern Hamilton faunas, but absent 

 from the Mississippian sea during later Devonian, Kinderhook, and Osage time 

 ■H It persisted in the Great Basin region and reappeared in the interior near Bates- 

 ville, Arkansas, in a limestone of the age of the St. Louis limestone; o and p, 

 Rhynchonella eurekensis Wale, a peculiar Great Basin species which occurs with 

 Leiorhynchus quadricostatum near Bates ville, Arkansas. Bryozoa: q, Archimedes 



[Continued on bottom of p, 533.1 



