PLATE LI— CouUnuwl. 



PuoNAx MissouRiENSis, Sliunuiid. 



Fi^ 33, 84. Doi-Mtl aiid profile views of an average example : showiut; tUe IiDeate striation of the Burface. 

 Choteau limestone. Pike county, MistouTi. 



LlORHYNCHUS (?) BOONENSIS, Sliumiud. 

 Fif . 35. Cardinal view of the biiijfe-plate ; sbuwiiitr itti median divinioii and the elevation of the crura. 



X 8. 



Cboteaa limestone. Cooper county, Missouri. ' 



PuGNAX Greenianus, Ulrich. 



Figs. 86-38. Front, profile and dorsal views uf an ialeriial ciist of an average individual ; showing' the 

 smooth latei-al slo^tes and faint plication of fold and sinus. 

 Keokuk group. New Albany, Indiana. 



PuGNAX Uta, Miircou. 

 Figs. 39-41. Doi-sal, profile and front views of an average adult shell. 



Fig. 42. The interior umbonal portion of the brachial valve ; showing the broad hinge-plate and narrow 

 median incision, X 3. 



Coal Measures. Manhattan, Kansas. 



PuGNAX EXPLANATU8, McCliesiiey. 

 Pigs. 43-45. Front, dorsal and profile views, diawn frum a sulphur east of the original specimen. 

 Kaskaskia limestone. Illinois. 



PuGNAX, sp. ? 

 Figs. 46-48. Profile, front and dorsal views of an undetermined internal cast. The shell has some points 

 of similarity to the Rhynchonella IllinoiseTisis, Meek and Worthen. 

 Coal Measures. Qrdham county, Texas. 



Genus HYPOTHYRIS, Kixg. 



I'ajtc lii.i. 



Hypothyris venostula, Hall (= Rhynchonella cuboides, Soworb}). 



Figs. 49, 50, 62. Cardinal, frontal and profile views of a typical specimen ; showing the subcuboidal fonn, 



low median fold and broad, deep median sinus. 

 Pig. 61. Front view of an internal cast with fewer plications, and showing the branches of the vascular 



trunks on the sinus. 

 Figs. 63, 54. Internal casts of i>edicle-valve8 ; showing the muscular impression, and some variation in the 



form of the vascular sinuses. 

 Pig. 55. An internal cast of the pedicle-valve, enlarged to show the system of vascular sinuses. X 2. 

 TuUy limestone. Ovid, N. T. 



