No. I.] LARVAL STAGES OF SCHLOENBACHIA. 257 



Steadily higher and narrower, changing gradually to the adult 

 characters, but with no sudden change to mark the stage. 



Ephebic or Adult. 



It would be purely artificial to divide the adult stage into the 

 three subdivisions ana-, meta-, and paraphebic, for the change 

 is too gradual. Near the beginning of the sixth whorl, at a 

 diameter of 12 mm., the nodes on the shoulder keels grow 

 stronger and form continuations of the ribs, bending forwards 

 over the intervening space to the ventral keel, and finally notch- 

 ing it. Since most species of Schloenbachia have this charac- 

 ter this may be considered as the beginning of the adult period. 

 These characters are seen sometimes as early as four and three- 

 quarters whorls, diameter of 10 to 11 mm. A general descrip- 

 tion of the adult stage has already been given under the 

 diagnosis of the species. The adult septa are figured on PI. 

 E, Fig. 5, at diameter 18.20 mm., and a cross-section of an 

 adult specimen on PI. C, Fig. 7, diameter 22.25 "^"^• 



Synopsis of Results. 



Schloenbachia oregotiensis is a remarkable species, in showing 

 its descent so well through its ontogeny ; the only other species 

 of which larval stages have been figured, 5. varicosa Sowerby, 

 figured by Branco in Palaeontographica, vol. xxvi, PI. E, Fig. 4, 

 shows the glyphioceran character at the third septum, the 

 Anarcestes, Tornoceras, and Prionoceras stages being omitted 

 by acceleration of development. The omission of stages occurs 

 just at this point, between the protoconch, which is always con- 

 stant in any one group, and the larval stages. A kindred form, 

 Oxynoticeras oxynotimi, reaches the glyphioceran stage at the 

 second septum, having skipped the preceding stages, but going 

 through the Gastrioceras, Paralegoceras, and Styrites stages 

 just as does Schloenbachia oregonensis. This seems to the 

 writer to have been due to the hatching of different genera or 

 species at different stages of growth, the omitted stages corre- 

 sponding to a period when the animal remained in the Q%;g after 

 formation of the protoconch. 



