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PL iii. They are somewhat enlarged and show the loose coiling of several genera 

 in the nepionic stages of development during this period of their evolution. Sub- 

 sequently the coiling becomes closer, as has been demonstrated by Branco. Fig. 

 20, Mimoceras compression ; Fig. 21, Anarcestes subnautilinus ; Fig. 22, Agonia- 

 tites bicanaliculatus, var. gracilis ; Fig. 23, Gephuroceras planorbe ; Fig. 24, 

 calculiforrne, and Fig. 25, sablamellosum ; Fig. 2,6, M antic oc eras latidorsale, 

 and Fig. 27, Glyphioceras diadema. 



Figs. 28 and 29. Protoconch of Orthoceras, after Clarke, Am. Geo/., xii, 

 August, 1893. 



Figs. 30 and 31. Protoconch of Bactrites, after Branco. 



