PLATE IV B— Continued, 



Orbicli-oidea Randalt.i, Hfill. 



Fitr. 18. The exterior of a pedicle-valve ; showing-, fi-om compi-ession, the ai)ical muscular ridge, the 

 radiating- pallial sinuses and the intei-nal ti-ack of the pedicle-fui-i-ow extending toward the 

 margin and interi-upting the concenti-ic gi-o\vth-lines. The overlapjiing marginal portion of the 

 opposite valve is seen about the posterior arc of the cii-cumference. Natural size. 

 Hamilton g)-oup. Near Srhoharic, N. T. 



Obiculoidea pulchra, .sp. IIOV. 



Fig. 19. The extei-ior of a pedicle-valve. X 1-5. 

 Cuyahoga shale. B^refii Ohio. 



Okbiculoidea Manhattanen.si.s. Meek and Hayden. 



Fig. 20. The intei-ior of a pedicle-valve ; showing the character of the pedicle-area, the radiating vascular 

 lines, and where the shell is broken on the antei'ior portion, the character of the external 

 oi-namentation and the unu.sual thickness of the valve. 

 Coal Measui'es. Riley comity. Kaiisa.i. 



GEHLERTELLA. s.-gen. nov. 



Page 120. 



Q5hlertej,la pleurites. Meek. 



Fig. 21. The iiitei-ior of a jiedicle-valve ; showing the elevated pediele-i-idge and the open, marginal fora- 

 men. Natural size. 

 Fig. 22. Pi-otile of the same, giving the intei-nal elevation of the pedicle-area. 



Figs. 23, 24. Brachial valves, differing sliglitly in outline, and showing the posterior position of the apex. 

 Waverly group. Newark, Ohio. 



LINDSTRGEMELI,A, s.-gen. nov. 



Page 1-20. 

 LiNDSTRCEMELLA ASPIDIUJI, sp. llOV. 



Fig. 25. A brachial valve, fi-om which the shell is largely exfoliated, but retaining sufficient to show the dis- 

 tinct, elevated, concentric ridges characterizing the external surface. The great lateral i-idges 

 and the faintej- median septum ai-e re'presented by fui-rows. At the postei-ior exti-emities of the 

 foi-mer are seen two small subcii-cular muscular impressions, while the scars of the anterioi- 

 adductors are strongly developed. Natural size. 



Fig. 26. The counterpart of the same ; drawn from a gutta-percha impression, showing all the internal 

 charactei-s in their natural relief. 



Hamilton group. Near Hamilton, N. T. 



Fig, 27. A natural cast of the exterior of a large pedicle-valve believed to belong to this species ; showing 

 the character of the surface ornamentation, and the peculiar undulation of the concentric lidges 

 on approaching the pedicle-area. The pedi(;le-pass=a.ge difl'ei-s from that in the normal matui-e 

 Okbiculoidea, in not l>eing closed, though its margins appear to be in contai;t. The charactei-s 

 of this area as represented in the di-awing, have been slightly restored fi-om other specimens. 

 Hamilton group. Near Leonardsville, N. Y. 



Fig. 28. A small pedicle- valve, with the characteristic oi-namentation and strongly developed foraminal 

 groove. 



Hamilton group. Near Darien, N. Y. 



RCEMERELLA, s.-gen. nov. 



Page 120. 



Rcemerella grandis, Vanuxem. 



Fig. 29. The exterior of a brachial valve. 



Hamilton limestone. Falls of the Ohio. 

 Fig 30. The interior of a pedicle-valve from which the shell has been partially exfoliated, exposing the 



matrix and the cast of the extei-nal pedicle-g-i-oove. 

 Fig. 31. The couuLei-part of the same specimen, fnmi a gutta-percha cast; sho-wing all the essential ex- 

 ternal characters. The extreme depression of the antei-ior portion of the valve and the cor- 

 respondingly great elevation of the pedicle-area are features subject to some slight variation 

 within the limits of the species. 



Hamilton gi-oup. Cazenovia, N. Y. 



