PLATE VI— Continuetl. 



RHIPIDOMELLA, CEhleut. 



rage iUS. 



Orthis Oweni. sp. IIOV. 

 (See Supplemeul I'or tiescriptioii.; 

 Fig. 19. The exterior of a bi-achial valve. 

 Figs. 20, 21. Interiors of pedicle and V)i-achial valves, respectively. 



" Knobstone gronp" of Owen, ^ age of the Waverly. BiMon-immUl Knuhs, Kentucky. 



SCHIZOPHOEIA, King. 



P.ige 211. 

 Okthls C.VniNATA, Hull. 



Pig. 22. An internal cast of a pedicle-valve; showing the character of the muscular area, at the antei-ior 

 margin of which are seen traces of the vascular sinu.ses. 

 Chemung gi'oui'). JS'ear Painted Post, N. Y. 

 For fnrtlipr illustration, see Palseontology of New York, Volume IV, jilate viii, figs. 30-32. 



Okthis Swallovi, Hall. 

 Figs. 23, 24. The exterior and infei-ior of the jiedicle-valve. 



Burlington limestone. Burlington, Iowa. 



Orthis Tulliensis, H;ill. 



Figs. 25, 26, 27. Three views of a normal individual ; showing the great convexity of the brachial valve 



and the shallow pedicle-valve. 

 Fig. 28. An internal cast of the brachial valve; showing the (piadrnple muscular impi-es.sion and the prin- 

 cipal vascular trunks. At y is the tilling of the I'ostral cavity of the opposite valve. 

 Fig. 29. An internal cast of the pedicle-valve. 



TuUy limestone. Keuka Lake, N. Y. 

 For further illustration, see Palteontology of New York, Volume IV, plate vii, tig. 5. 



Orthis propinqua, Hall. 



Fig. 30. An internal cast of the brachial valve. The subdivision and the course of the vascular sinuses 

 are very sharply I'etained. 



Coi-niferous limestone. Avon, N. Y. 

 For further illusti-ation, see Palaeontology of New York, Volume IV, plate v, fig. 3. 



Orthis impres.sa, Hall. 



(.See Plate VI .\, tigs. 26, 27.) 

 Fig. 31. An internal cast of the pedicle-valve ; showing the subdivisions of the muscular area, and the un- 

 usual arrangement of the vascular sinuses. 

 Chemung gi'oup. 

 For further illustration of this species, see Palffiontology of N.Y., Volume IV, pi. viii, tigs. 11-19. 



ORTHOSTROPHIA, Hall. 



Page 199. 



Orthis strophomenoides, Hall. 



(See Plate Va, tigs. 24-27.) 

 Fig. 32. The exterior of an imperfect brachial valve. 



Fig. 33. An internal ca.st of the pe<licle-valve ; .showing the vei'y small muscular area, the ovarian mark- 

 ings in the uml)o-lateral regions, and the vascular sinuses over the pallial region. 

 Fig. 34. An internal cast of the bi-achiai valve, retaining the impression of the simple cai-dinal process, and 

 showing the four sliarply defined adductor scai-s, the ovarian markings and the ramified vascu- 

 lar sinuses. 



Lower Ilelderberg group. Near Clarksville, N. Y. 



