PLATE III. 



TjffjcMnl. I. Latinals. 



c. Centrals. 



sc. Suboardinals oi' jjostmcdians. 

 v.v. Crescent. 



e. Externals. 



X. Composite i>osterioi-s. 

 P. Pedicle-gi'oove. 

 F Foramen. 



t'. Forauiinal pits. 



-s. Septum (median), 

 s'. Septum (lateral). 

 o. Vascular trunks (oviducts?). 

 d'. Subapical area, 

 cb. Cardinal bosses. 

 fc. Foramina! callo.sity. 



LKPTOBOLUS, Hall. 



P.ige 73. 

 LePTOBOLUS IN.SIGNIS. Hall. 



[■"ij.'. -1. .'\n internal cra.st df a jiedicle-valve ; showing- the \cmg, cni-ved lateral scars and a faint indii-atinn 



ot the piisterioi' mn.s( ular depiession. X H^. 

 Flu-. '2. Aw internal ifast of the brachial valve, .similarly enlarged, and showinfr the median septum and 



two lateral grooves, which cdricspond either to the scars (z) seen in tig. (i, or to the lateral septa 



(sO in tig. 10. 



Utica sl.ite. Holland Patent, JV. Y. 

 l'"ig. 3. The exteiior nf the shell ; showing the concentric and radiating striie. X S. 



Utica slate. Middlevillt, jV. 1'. 

 Kiir. 4. The interior of a pedicle valve ; showing the cai-dinal area ami groove, and the thick, eallouseil 



fulcra of the lateral muscles. X IS. 

 Kig. 5. Ajiothei- interior of this valve, in which the transverse extensions of the lateral fulcra are <-.(intinu- 

 cius. The iiosti'i'i<n' dei)res.se<l ai-ea bears the impression of the centi-al muscles, and indications 

 of a subdivi.siou of the pitted su;face into dift'erentiated scars. X 15. 

 Fig. ti. The interior of a brachial valve : showing the gi'Ouved ai-ea, conspicuous median septum and faint 

 latei-al scars. 



Hudson Rivei- group (Utica horizon). Cimtigion, Kentucky. 



Leptobolu.s occidentali.s, Hall. 



Fig. 7. The exterioi- of the ."ihell. X S. 



Hark shale of the Utica hoi-izon. Hnwhy'f: Mill, 12 miles north-west of JJiiAmque, Iowa. 



Leptobolus lepis, Hall. 



Fig. S. The interioi- of a [ledicle-valve ; showing the cardinal groove and the diverging .septa. X 12. 

 Fig. n. A cast of the interior of the pedicle-valve ; showing the central scar and the transvei-se extension 



of the laterals. X 12. 

 Fig. 10. The interior of the brachial valve ; showing the grooved cardinal .-irea and the median and latei-al 



se]ita, each of which is bifurcate at its extremity. X 12. 

 Hudson River grouji. Lickinfi liivt-r, Ohio. 



SCHIZOBOLUS, Ulrich. 



Page 87. 

 SCHIZOBOLUS TRUNCATUS, Hall (^p.). 

 Fig. 11. The exterior of a pedicle-valve. X 3. 



Genesee slate. WealKrn New York. 

 Fig. 12. The interior of a jiedicle-valve, drawn from one of Mr. Ui.iuch's original si)ecimens; showing the 

 pe<licle-slit, the comj)Osite muscular scars abidting against the median septum, and the long, 

 curveQ lateial seal's. X 5. 



Black slate (Genesee). Madisan county, Kentucky. 

 Fig. IS. The extei-ior of the bi-achial valve. X 3. 



Gene.see slate. iVe.'itern New York. 

 Fig. 14 The interior of the brachial valve ; showing the septum and faintly defined muscular iinjires.sions. 

 X •'). 



Ulack slate (Genesee). Madison county, Kentucky. 



