PLATE IV i— Continued. 

 OUBICULOIDEA NkWBKKKYI, IIull. 



Fig. IS. The same fenlures ; showin;^- the' strung- eleviition of the area, but the absence of callosities, the 

 larg-e tbiamen, the sharply deKneil, though flattened median ridge and lateial walls of the 

 pedicle-passag-o. X 3. 



Waverly group. Ciiyafioga JFhlls, Ohio. 

 (Fi-om the original locality, a ferruginous band about 110 feet below the conglomerate.) 



CEIIbERTKLLA s.-gen nov. 



Page 120. 

 Q^HLERTELLA PLEURITES, Mook. 



Fig. 19. The internal characlei-s of the pedicle-area; showing the open marginal foramen, the elevated, 

 radially striated lateral walls, the median rid^-e and a short apical septum. X 3. 



Fig. 20. The same features fi-om a .other .specimen, in which the walls of the area are smooth and the apicuil 

 septum absent. X 3. 



Waverly group. Newark, Ohio. 



ORBICULOIDEA, D'Orbignv. 



Page liO. 



Okbiculoidea Lodensi.s, VaiHi.xeiii. 



Fig. 21. The internal characters of the ]iedicle-area; indicating the unusual bi'eadth and depth of the base 

 of the groove and the low lateral walls ; also the interruption in the ornamention of the shell 

 from the foramen outwards, prol)al)ly indicating the line of union of the primitive margins of 

 the apertnre. X 4. 



Genesee shale. Lodi, N. Y. 



Oitisicui.oiDEA, ^[1. iiidet. 



Fig. 22. A natural cast of the interior apical portion of the brachial valve ; showing the anterior and pos- 

 tei-ior muscular riilges. X B 



(!;hemimg group. Warren. Pa. 



Okbicui>oidea ^'ITIDA, Phillips. 



Fig. 23. The pedicle-area of an extremely young shell, having a diaraetei' of 1 mm. The foramen is a 

 mai-giual slit extending, with divergent edges, for almost the entire I'adius of the valve. At 

 the apex, the pedicle-gnove appears in an incipient stage. X 50. 

 Fig. 24. A considerably later stage of development of these parts, the diameter of the shell being .■) ram. ; 

 showing the mai-ginsof the foramen united for most of their length, but still sei)arated at the 

 jiosterior <'dge tif the valve. The sti'ucture of the area is .somewhat oliscured by the compres- 

 sion of the specimen. X 12. 

 Fig. 25. A later stage of growth, exhibited by a specimen 7 mm. in diameter. Here the angles made by 

 the edges of the foramen with the posterior edge of the shell are acute and approximate. The 

 l)e(iicle-groove has jn'ogiessed so as nearly to till the entire hiatus. X "i 

 Figures 23-25 are from a block of black shale upon which valves of this .species are crowded in 

 great numbers, to the exclusion of other fossils. The condition of the pedicle-area in its lati^r 

 develoi>ment, as shown in the following tigni-es, is also amply represented in these specimens. 

 Lower Coal Mcasnivs f^prhiyfitlil. lllininK. 

 The intei-nal pedicle-area of asnnill but nniture individual; showing the base and lateral walls 



of the groove .and the slight callosity at the apical extremity. X 7. 

 The external surface of a similar specrimen ; showing the general form of the groove at maturity, 

 and the absence of any fui'row or intei-ruption of the concentric ornamentation beyond its jios- 

 terior extremity. X 7- 

 The entire valve, of which tig. 27 lepresents the pedicle-ai'ea. X 2. 



Coal Measures. Grover, Mii^souri. 

 The interior of a pedicle-valve ; showing the Iiase of the groove, the foramen and the muscular 

 impressi(ms. (After Davidsoi!. Brit. Carb. Brach., Suppl., pi. xxx, fig. 13 n.) 



Orbiculoidea, sp.. Mock. 



Fig. 31. " An imiires.«ion of the outside of till! under valve in the matrix (slightly le.=s than natural size). 



with jiortions of the thin shell adhering, so as to show the smooth inside, ami a piominent 



internal ridge, conesponding to a deep (external furrow, with a .small, rounil or oval foramen 



at its outer end." (Meek, Palstology of Eastern Nebi'aska, plate iv, tig. 3, and Explanation.) 



Coal Measures. Xcar Xthra.'<ka Citi/, Neh. 



