520 



GEOLOGY. 



Fig. 235. — The Kinderhook (Lower Mississippian) Fauna. Gastropoda: a, Por- 

 cellia nodosa Hall, a shell coiled nearly symmetrically in a plane; b, Straparollus 

 obtusus Hall, a low spiral shell; c, Macrocheilus blairi (M. and G.), a shell with 

 a moderately elevated spire; d, Platyostoma broadheadi S. A. M., one of the capulid 

 shells; all four of these genera are present in the Devonian. Crinoidea: e, Actino- 

 crinus senectus M. and G., a camerate crinoid belonging to the family Actinocrinidce, 

 all the members of which are peculiarly Mississippian; /, Dichocrinus inornatus 

 W. and Sp., one of the earliest crinoids with only two basal plates. No such 

 type of crinoid base is known anywhere earlier than the Mississippian. With the 

 Devonian, crinoids with four basal plates disappeared, and in the Mississippian, 

 only those with two and three basalsare present. Corals: g, Leptopora placenta 

 (White), a peculiar compound coral whose relationships are not well understood. 

 Trilobite: h, Proetus ellipticus M. and W. Trilobites are rare in the Kinderhook 

 and the one here illustrated is a good example of their lack of ornamentation. 

 Cephalopoda: i, Muensteroceras oweni (Hall), one of the abundant species in the 

 famous Kinderhook goniatite bed at Rockford, Ind. ; /, Prodromites gorbyi (S. A. M.). 

 This genus has a wide geographic distribution in the Kinderhook, and is the earliest 

 form to show secondary lobing of the sutures. Brachiopoda: k, Spirifer biplicatus 

 Hall, a member of the genus retaining a greatly elongate hinge-line, a character 

 which was pronounced among Devonian members of the genus, but not among 

 Mississippian species; I, Spirifer marionensis Shum., a species related to such 

 species as S. disjunctus of the Devonian (see Fig. 212, p. 476) in its plicated fold 

 and sinus, but it shows an advance in the bifurcating plications upon the sides 

 of the shell; m, Cyrtina acutirostris (Shum.), a species of a Devonian genus, no 

 members of which persist beyond the lower Mississippian; n, Productella pyxidata 

 Hall, a representative of a genus which had its great development in the later De- 

 vonian, only a few forms being present in the Mississippian; o, Productus arcuatus 

 Hall; the genus Productus is an outgrowth from the earlier Productella, and is 

 peculiarly characteristic of the Mississippian, Carboniferous, and Permian faunas; 

 p, Paraphorhynchus striatocostatus (M. and W). A striated rhynchonelloid shell 

 characteristic of the lower Kinderhook horizons of Iowa, northern Missouri and 



[Continued on bottom of p. 521 J 



