616 



GEOLOGY. 



z bb cc ee it gg hh 



li 



Fig. 286. — The Pennsylvanian (Coal Measures) Fauna. Pelecypoda: a, Allorisma 

 subcuneata M. and H., b, Schizodus wheeleri Swall., c, Monopteria longispina Cox, 

 d, Myalina recurvirostris , M. and W., e, Aviculopecten occidentalis Shum., /, Avi- 

 culopecten carboriiferus Stev. ; a group of six pelecypods of types [more or less 

 common in the Pennsylvanian; their relationships for the most part are with 

 forms in the Mississippian faunas. Gastropoda: g, Bellerophon percarinatus 

 Con., h, Worthenia tabulata (Con.), i, Meekospira peracuta (M. and W.), j, Nati- 

 copsis altonensis McCh., k, Trachydomia wheeleri (Swall.); a group of gastropods 

 showing a variety of forms. These Carboniferous members of the class agree 

 with their ancestors in the entire apertures, the canaliculate aperture so com- 

 mon in recent marine gastropods being introduced later. Trilobita: I, Phillipsia 

 major Shum., almost the last of the trilobites; this genus persists into the Per- 

 mian, and then becomes extinct. Crinoidea: m, Hydreionocrinus acanthoporus 

 M. and W., showing the extravagant development of the ventral sack; n, Eupachy- 

 crinus magister M. and G., with biserial arms, a type of arm structure introduced 

 late in the history of the Inadunata, but very early in the Carrier ata. This form 

 approaches some of its Mesozoic relatives, especially such Triassic forms as Encrinus. 

 Coral: o, Zaphrentis gibsonii White. Corals are rare in this fauna, and are nearly 

 all of the horn-shaped genera. Protozoa: p, Fusulina secalicus Say, a little 

 foraminifer that sometimes constitutes nearly the entire calcareous material of 

 important limestone beds. It occurs abundantly in America, Asia, and Europe. 

 Cephalopoda: q, Paralegoceras news^mi Smith, r, Orthoceras cribrosum Gein., s. 

 Temnocheilus forbesianus (McCh.); three figures representing three types of ceph- 

 alopods in the Carboniferous, viz.: (1) the goniatites, with their lobed sutures 

 which gave rise to the Mesozoic ammonites; (2) the straight orthoceratites which 



