PLATE Xlill.— Continued. 



Page. 



Figs. 59 and 60. Ctenodonta socialis, n. sp 594 



59. Outline views of three specimens ot different sizes and showing slight variations in form. 

 80. Hinge of two right valves, X S, showing slight differences inthe anterior parts. 



Figs.61 to 64. CtenodSujta CALViNi, n. sp 596 



61. An excellent cast of the interior of a left valve, showing muscular scars and rays more plainly than 



usual. In this specimen the length also is a little greater than in the others. 



62. Another cast of a left valve. Minn. G«ol. Sur. Mus. Eeg. No. 8628. 



63 and 64. Lateral and cardinal views of a cast of a right valve, representing the usual characters of the species. 



Figs. 65 and 66. Ctenodonta madisonensis, n. sp ._ 597 



The left side and an anterior view of a testiferous example of this species. 



Figs. 37 to 73. Ctenodonta PECCNDA Hall 595 



67 and 68. The right side and an anterior view of a cast of the interior. In many specimens the posterior 

 margin is more rounded 

 69, A small part of the external surface magnified to show the fine concentric and radiating lines. 

 70 to 72. Cardinal and anterior views and the right side of a specimen preserving the shell. 



73. The wavy hinge line as shown on a cast of the interior, X 5. 



Figs. 74 and 75. Ctenodonta simulatrix, n. sp 600 



74. A cast of the interior of a right valve, showing the muscular scars and retaining a little of the shell 



about the heak. 



75. As much of the hinge as can be made out from the preceding specimen. 



Figs. 76 to 82. Ctenodonta ALBEBTINA, n. sp '. 598 



76 to 78. Three views of a large specimen having the posterior end a little narrower than usual. 



79. A smaller specimen of the usual form. 



80. Hinge of a large and smaller right valve, showing the subrostral pit and the geniculated teeth. 

 81 and 82. Cardinal and lateral views of a cast ot the interior which retains a part of the hinge, 



\ 



Figs.83 to 87. Ctenodonta OBLiQffA Hall 604 



83 and 84. Lateral and cardinal views of a small specimen of the large northwestern variety of this species, X 5. 

 As usual, the specimen is a cast of the interior and shows the muscular scars and Impressions of the 

 hinge denticles very clearly. 

 85 to 87. Three internal casts of a small form of the species from the Cincinnati group of Ohio, X 5. 



■Figs.88 to 90. Ctenodonta COMPRBSSA Ulrioh 600 



(See also plate xxxvn, fig. 29.) 

 88 and 89. Posterior and lateral views of a left valve. 



90. The greater part of the hinge of another left valve, X 5, shoeing the various parts in a. beautiful 

 state of preservation. 



Figs 91 and 92. Ctenodonta hambcroensis Walcott 605 



A right(?) valve of the natural size and X 5. 



Figs. 93 and 94. Ctenodonta alta Hall 602 



Lateral and posterior views of a cast of the interior. 



Figs.95 to 97. Ctenodonta intermedia TJlrlch 601 



95 and 96. Lateral and posterior views of a right valve preserving much of the shell. The opposite valve is 

 restored In the profile view. 

 97. A sharply marked cast of the interior of a left valve. In this specimen t)ie posterior extremity is 

 unusually produced. 



Figs. 98 to 101. Ctenodonta BECURVA TJlrlch 603 



98 to 100. Posterior, lateral and cardinal views of a perfect specimen of this species, showing the usual form, 

 the anterior sulcus and the sharply defined anterior and posterior lunettes. 



101. The greater part of a hinge of a left valve, X 2, showing the arrangement of the denticles, the 



sharply elevated outer margin and the llgamental area on the right side of the beak. 



Figs.102 to 106. Ctenodonta SIMII.I8 Ulrich 604 



102. Hinge of a left valve of this species, X 2, showing the principal features upon which this species is 



separated from V. recurva, (See fig. 101.) 



103. The left side of a specimen, showing the usual form of the species. Minn. Geol. Sur. Mus. Beg. 



No. 8368. 

 104 to 106, Lateral, cardinal and posterior views of a specimen having an outline very similar to that of 

 0. recurva. But the absence of the anterior sulcus, the greater convexity of its valves and the 

 less sharply defined lunettes are all characteristic of C. stmilis and prove its distinctness from 

 C. recurva. 



