PLATE XXIII. 



(Fipires 1-18 by B. I'. Whitpibld.) 



Le^nd : A. Cardinal ai-ea, )>edicle-valve. x', MiiRciilar cavity, 



a'. Inner division, pedicle-valve. r. Diductor wears, 



a". Outer division, |>edicle-valve. j. Canlinal process. 



F. Delthyrium. b. Dental sockets. 



s'. Apical callosity. a. AnteHor adductors, 



d. Dental lamellae. a'. Posterior adductor?. 

 X. Pedicle-cavity. 



Genus SPIKIFER, Sowerby. 



Page 1. 



Spieifer gkanulosos, Conrad. 



Fig^. 1. Dorsal view of a normal adult, retaining the shell. 



Fig. 3. The interior of a j>edicle-valve ; showing the apical callosity in the delthyrium and the character 

 of the muscular area. 



Fig. 8. The interior of a brachial valve ; showing the articulating apparatus and muscular ai-ea. 



Fig. 4. An enlargement of the surface ; showing the papillose character of the shell. 



Fig. 6. The central portion of a cast of the brachial valve ; showing the striated cardinal process and the 

 two pairs of ad<luctor scars. X 2. 



Fig. 6. A similar view of another specimen. 



Fig. 7. A cast of the muscular area of the pedicle-valve with the muscular impression unusually elongate. 



Fig. 8. A similar view of a larger specimen. 



Fig. 9. Another view of the same parts, the muscular area being proi>ortionally shoi-ter and smaller than 

 in the preceding figui-e. 



Fig. 10. A view of the same characters in another example. All these specimens show variations in the 

 form of the muscular area, the size of the adductor scars as well as different degrees of devel- 

 opment of the callosity of the delthyrium. 



Rg. 11. A portion of the muscular area of the pedicle-valve ; showing its surface markings and the dis- 

 tinction between the diductor and adductor scai-s. X 2. 



V\g. 13. A profile of an internal cast of the pedicle-valve ; showing the filling of the rostral and muscular 

 cavities. 



Fig. 13. Similar cast of another pedicle-valve with a more elevated muscular impression. 



Fig. 14. An enlargement of a partly exfoliated surface. 



Hamilton shales. Western New York. 



Fig. 15. An enlargement of a worn surface. The coarse punctations are not structural but probably due 

 to some Iwring sponge. 



Hamilton group. Cumberland, Maryland. 



Spikifer mackothykis, Hall. 



Fig. 16. The exterior of a full-grown individual. 



Fig. 17. A cardinal view of an imperfect specimen ; showing the elevation of the'valves. 

 Fig. 18. An enlargement of the surface ; showing the crenulate margins of the concentric lamellse. 

 Comiferous limestone. Near Columbus, Ohio. 



