PLATE III. 



Legenil. I. Latei'als. 

 c. Centrals. 



sc. Subcardinals o)' ijostmediaris. 

 or. Crescent. 

 ' e. Exteraals. 



X. Composite jiostei-iors. 

 P. Pedicle-groove. 

 F Foramen. 



F\g. 

 V\g. 



Kig. 



Fi(r. 

 Fig. 



f. Foiaminal pits. 



s. Septum (median), 



s'. Septum (lateral). 



o. Vascular ti-unks (oviducts?), 



d'. Subapical area, 



cb. Cardinal bosses. 



fc. Forarainal callosity. 



LEPTOBOLUS, Hall. 



Page 73. 

 LeI'TOBOLUS INSIGNIS, Hall. 



1. An internal cast of a pedicle-valve ; showing- the long, curved lateral scars and a faint indication 



of the postei'ior muscular depression. X 10. 



2. An internal cast of the bi'achial valve, similarly enlarged, and showing the median .septum and 



two latei-al grooves, which correspond either to the scars (z) seen in fig. 6, or to the lateral septa 

 (s') in fig. 10. 



Utica slate. Holland Patent, N. Y. 

 'J'he exteiior of the shell ; showing the concentric and radiating stria;. X S. 



Utica slate. Middleville, jY. Y. 

 The intei-ioi- of a pedicle valve ; showing the cai-dinal area and gi'oove, and the thick, calloused 



3 



4 



fulcra of the latei-al muscles. 

 Another interior of this valve 



oua. The posterior depi'essed area bear.s the impression of the central muscles, 



X 1.0. 

 in which the ti-ansverse extensions of the lateral fulcra are continu- 



Fig. 7. 



d indications 

 of a subdivision of the jiitted suiface into differentiated scars. X 15. 

 The interior of a Vjrachial val%e ; showing the grooved area, conspicuous median septuin and faint 

 lateral scars. 



Hudson Rivei- group (Utica horizon). Com/ngton., Kentucky. 



Leptobolu.s OCCIDENTALIS, Hilll. 

 The exterioi' of Ihe shell. X S. 



Dai-k shale of the Utica horizon. Hawley'a Mill. 12 miles imrth-west of Duhuqne, lovM. 



Leptobolus lepis, Hilll. 



Fig. 8. The inlerioi- of a pedicle-valve ; showing the cardinal groove and the diverging septa. X 12. 

 Fig. 9. A cast of the interioj- of the pedicle-valve ; showing the central scar and the transverse extension 



of the laterals. X 12. 

 Fig. 10. The interioi- of the brachial valve ; showing the gi-ooved cardinal area and the median and lateral 



septa, each of which is bifurcate at its extremity. X 12. 

 Hudson River grouij. Licking River, Ohio. 



SCHIZOBOLUS, Uleich. 



Page 87. 

 SCHIZOBOLUS TKTJNCATUS, Hall (sp.). 



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



Genesee slate. Westeiii New York. 

 Fig. 12. The interior of a pedicle-valve, drawn from one of Mr. Ulrich's original specimens ; showing the 

 pedicle-slit, the composite muscular scars abutting against the median septum, and the long, 

 curved lateral scars. X 5. 



Black slate (Genesee). Madison county, Kentucky. 

 Fig. 13. The extei'ior of the brachial valve. X 3. 



Genesee slate. Western New York. 

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

 X 5. 



Black slate (Genesee). Madison county, Kentucky. 



