XII LIST OF ILLUSTRATIONS. 



Page. 



Left valve and side and edge views of another left valve of Bollia regularis 

 (Emmons). Left valve of Beyrichia buchiana Jones 288 



A left valve of Beyrichia tuberculata, with the lines of a Drepanella drawn over it. . 290 



Right valve of Drepanella macra Ulrich. Left valve of Beyrichia tuberculata 

 (Kloeden). Right valve of Drepanella crassinoda Ulrich for comparison with 

 left valve of Beyrichia noetlingi Reuter. Left valve of Drepanella nitida 

 (Ulrich) for comparison with the corresponding valve of Beyrichia baueri 

 Reuter 291 



Left valve of Drepanella richardsoni (Miller). Right valve of Beyrichia tumida 

 (Ulrich). Right valve of Beyrichia la ta Hall. Right valve of Treposella lyoni 

 (Ulrich) ' 292 



Right valve of Ctenobolbina subcrassa Ulrich. Right valve of Beyrichia plicata 

 (Krause). Left valve of Beyrichia reuteri Krause. Right valve of Beyrichia 

 salteriana Jones. The figures illustrate the relation and probable derivation 

 of the Beyrichia salteriana group from a Ctenobolbina like subcrassa 293 



Left valve of Beyrichia clavata Kolmodin. Left valve of Beyrichia granulifera, 

 new name. Right valve of Beyrichia tumida (Ulrich). The figures illustrate 

 the resemblance of the Beyrichia clavata group to the B. interrupta group and 

 show the similar antero- ventral prolongation of the posterior lobe 294 



Left valve of Beyrichia (Steusloffia) linnarssoni (Krause). Right valve of 

 Strepula concentrica Jones and I loll . Left valve of Strepula irregularis Jones 

 and Holl. Left valve of Beyrichia ( Tetradella?) erratica Krause. Left valve of 

 Strepula? lineata granulosa Steusloff. Shows similar development of superfi- 

 cial linear crests in Steusloffia and Strepula 296 



Left valve of Ctenobolbina umbonata (Steusloff). Right valve of Ctenobolbina 

 fulcrata (Ulrich). Right valve of Ctenobolbina impressa (Steusloff). Left 

 valve of Ctenobolbina subcrassa Ulrich. Left valve of Beyrichia (Steusloffia) 

 antiqua (Steusloff). Left valve of Beyrichia (Steusloffia) acuta (Krause) 297 



Right valve of Beyrichia reticulata (Krause), and the same valve of Eurychilina 

 reticulata (Ulrich), showing the similarity of the two forms referred to in the 

 text 298 



Right valve of Bey rich in interrupta (Jones). Left valve of Beyrichia v-scripta 

 (Krause). Right valve of Eurychilina subradiata Ulrich. Left valve of Bey- 

 richia clavata Kolmodin. Left valve of Beyrichia (Steusloffia) acuta (Krause). 

 The illustrations show possible derivation of the Beyrichia interrupta group 

 ' from Eurychilina and its relation to the Beyrichia clavata group and to Steus- 

 loffia 299 



Right valve of Klcedcnia wilckensiana (Jones) (female individual), and Beyrichia 

 salteriana Jones, respectively, showing the relation of Kladenia to the B. sal- 

 teriana group. Left side, end, and ventral views of complete carapace of 

 Klcedenella pen nsylvanica (Jones) . Right and left valves of Klaidenia nearpassi 

 (Weller). Left and right valves, the latter a female form, of Kyammodcs 

 kiesowi (Krause). Left valve and anterior view of complete carapace of 

 Kyammodes whidbornei Jones. The similarity of Klcedeniu, Kladenclla, Kyam- 

 modes, and 1 he Beyrichia salteriana group are shown in the above figures 304 



Lefl valve of Bollia symmetrica (Hall). Right valve of Klcedenella halli (Jones). 

 Right valve of Klcedenella turgida, new species. Right valve of Beyrichia ? par- 

 allels Ulrich. These figures illustrate the similarity of expression of Bollia to 

 Klxdenella, and the possible derivation of Klcedenella from the Richmond 

 species Beyrichia '.' parallela 319 



( 'eratosaurus nasicornis. Right side of skull 360 



( 'eratosaurus nasicornis. Skull seen from 1 he left side 'Mi 1 ) 



( 'eratosaurus nasicornis. Skull seen from the right side. 361 



