• PLATE VIII. 



Cyrtina lachrymosa, Hall. 



Page 358. 



Figs. 1, 2. Views of an average example ; showing the riegular, slightly- 

 incurved cardinal area, and the sparsely pustulose exterior, x 2. 



Fig. 3. An enlargement of the exterior; showing the large pustules of various 

 sizes. X 5. 

 Waverly group. Richfield, Ohio. 



Cyrtina neogenes, Hall. 



Page 372. 



Fig. 4. The pedicle- valve broken so as to show the median septum supporting 



convergent dental plates. 

 Fig. 5. An internal cast of the pedicle-valve. 

 Fig. 6. Cardinal view of the "same specimen; showing the convergent dental 



plates uniting with the median septum. X 2. 

 Fig. 7. An enlargement of the external surface; showing the bases of concen- 

 tric rows of spinules. x 4. 

 Fig. 8. An enlargement of a portion of the interior of the pedicle-valve; 

 showing the convergence of the dental plates and the projection of the 

 median septum beyond their union. X 3. 

 Chert of the Burlington limestone. Burlington, Iowa. 



Cyrtina ttmbonata, Hall, var. Alpenensis, Hall. 



i;»age 357. . 



Figs. 9, 10. Views of an individual of normal size. 



Fig. 11. The conjoined valves split along the median septum ; showing the 

 extreme extension of the latter, its acute anterior extremity, and the pene- 

 tration of its median edge beyond the base of the dental lamellae. 



Fig. 12. Front view of a preparation ; showing the normal shape of the spiral 

 cones, and the form of the crura and loop. X 1^. 



Fig. 13. A lateral view of another preparation showing the extension of the 

 spiral into the rostral cavity divided by the median septum, and the pro- 

 jection of the loop downward and toward the brachial valve, x 1|. 

 Hamilton group. Alpena, Michigan. 



Syringothyris Missouri, Hall. 

 Page 358. 

 Figs. 14, 15, 16. Three views of the original specimen; showing its small size, 

 elevated pedicle-valve, broadly rounded cardinal margins and coarse 

 lateral plications. 

 Choteau limestone . Pike county, Missouri. 



388 



