PLATE IVr— Continaed. 



OiiBicuLOiDEA Newberryi, Hall. 



Fig. 18. The same features ; showing- the strong elevation of the area, but the absence of callosities, the 

 large foi'amen, the shai-jjly defined, though flattened median ridge and lateral walls of the 

 pedicle-passage. X 3. 



Waverly gi-oup. Cuyahoga Falls, Ohio. 

 (From the original locality, a femiginous Vjand about 110 feet below the conglomerate.) 



GEHLERTELLA s.-gen nov. 



Page 120. 



CEhlertella pleurites, Meek. 



Pig. 19. The internal characters of the pedicle-area; showing the open marginal foi'amen, the elevated, 

 radially striated lateral walls, the median ridge and a short apical septum. X 3. 



Fig. 20. The same features from a lOther specimen, in which the walls of the area are smooth and the apical 

 septum absent. X 3. 



Waverly group. Newark, Ohio. 



ORBICULOIDEA, D'Orbigny. 



Page 1-20. 



Orbicdloidea Lodensis, Vamixem. 



Fig. 21. The internal characters of the pedicle-area; indicating the unusual breadth and dejith of thebase 

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

 from the foramen outwards, probably indicating the line of union of the pi-imitive margins of 

 the apertxire. X 4. ..i-:.- -m 



Genesee shale. Lodi, N. Y. 



Orbiculoidea, .sp. indet. 



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

 terior muscular ridges. X 3 



Chemung group. Warrai, Pa. 



Orbiculoidea nitida, Philliiis. 



Pig. 23. The pedicle-area of an extremely young shell, having a fliameter of 1 mm. The foramen is a 

 marginal slit extending, with divergent edges, for almost the entire i-adius of the valve. At 

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



Fig. 24. A considerably latei' stage of development of these parts, the diameter of the shell being n mm. ; 

 showing the margins of the foramen united for most of their length, but still separated at the 

 posterior edge of the valve. The structure of the area is somewhat obscured by the compres- 

 sion of the specimen. X 12. 



Pig. 25. A later stage of growth, exhibited by a specimen 7 mm. in diametei-. Hei'e the angles made by 

 the edges of the foiauien with the postei-ior edge of the shell are acute and approximate. The 

 pedicle-groove has progi'essed so as nearly to till the entii-e hiatus. X "i 

 Figures 23-25 are fr(mi a block of lilack shale upon which valves of this species are crowded in 

 great numbei'S, to the exclusion of other fossils. The condition of the pedicle-ai-ea in its latei- 

 development, as shown in the following figui'es, is also amply j'epresented in these specimens. 

 Lower Coal Measui-es, Springfield. Illinois. 



Fig. 26. The intei'ual pedicle-ai-ea of a small but mature individual ; showing the base and lateral walls 

 of the gi'oove and the slight callosity at the apical exti-emity. X 7. 



Fig. 27. The external surface of a similar specimen ; showing the genei'al form of the groove at matui-ity, 

 and the absence of any fui'i-ow or interi'uption of the concentric oi'namentation beyond its pos- 

 terioi' extremity. X 7. 



Fig. 28. The entire valve, of which fig. 27 represents the pedicle-area. X 2. 

 Coal Measures. Gh'ovei; Mi.'ssouri. 



Fig. 29. The interior of a pedicle-valve ; showing the base of the groove, the foramen and the musculai- 

 impressions. (After Davidson. Brit. Carb. Brach., SuppL, pi. xxx, fig. 13 a.) 



Orbiculoidea, sp.. Meek. 



Fig. 31. "An impression of the outside of the under valve in the matrix (slightly less than natural size), 



with portions of the thin shell adhering, so as to show the smooth inside, and a prominent 



internal i-idge, corresponding to a deep external furi-ow, with a small, round or oval foramen 



at its outer end."' (Meek, Patetology of Eastern Nebraska, plate iv, fig. 3, and Explanation.) 



Coal Measures. Near Nebra.^ka City, Neh. 



