No. I.] LARVAL STAGES OF SCHLOENBACHIA. 25 1 



it with nine septa, diameter 0.68 mm., and three-quarters of a 

 coil; Fig 9 shows this same stage at a little over three-quarters 

 of a coil, diameter 0.74 mm., and its septa are shown on PI. D, 

 Fig. I . These figures show a gradually increasing height of the 

 whorl as compared with the width. The glyphioceran stage lasts 

 up to a diameter of i mm., and about one and one-quarter coils, 

 near the end of which stage, at diameter of 0.80 mm., a deep 

 sulcation or constriction makes its appearance ; this distinctively 

 glyphioceran character was observed on a large number of speci- 

 mens near the end of the first whorl, and never after that. 



Gastrioceras stage. — Near the beginning of the second 

 whorl, at diameter of a little over i mm., and after the appear- 

 ance of the constriction, the umbilicus begins to widen, until 

 at diameter of 1.20 mm. it is proportionally wider than in any 

 species of GlypJiioceras ; this is shown on PI. A, Figs. 10 and 

 II, one and three-eighths coils, and is transitional to Gastri- 

 oceras, a genus especially characteristic of the Upper Carbonif- 

 erous. A somewhat larger specimen, diameter 1.33 mm., one 

 and five-eighths whorls, is shown on PI. A, Figs. 12 and 13. 

 As the size increases the shape becomes more decidedly gas- 

 trioceran, as shown on PI. A, Figs. 14 and 15, one and seven- 

 eighths coils, diameter 1.65 mm.; the septa of this are seen on 

 PI. D, Fig. 2. This stage corresponds to that group of Gastri- 

 oceras that lacks the umbilical ribs and has the second lateral 

 lobe on the sides of the shell, as in Gastrioceras illinoisense 

 Miller and Gurley,^ of the Coal Measures. 



Paralegoceras stage. — The gastrioceran stage lasts from 

 near the beginning of the second whorl, diameter a little over 

 I mm., up to two and one-eighth whorls, diameter 2.15 mm., 

 when a third lateral lobe appears on the umbilical border; 

 then the whorl becomes higher and narrower, and the whole 

 aspect of the shell is like Paralegoceras Hyatt, a genus espe- 

 cially diagnostic of the Upper Carboniferous, and supposed to 

 be a direct descendant of Gastrioceras? This stage is shown 



1 Bulletin XI, Illinois State Mus., N. H., p. 42, PI. V, Figs. 6-8, 1896. 



2 For the relations of Glyphioceras, Gastrioceras, and Paralegoceras, see paper 

 by the writer, " Marine Fossils from the Coal Measures of Arkansas," Proc. Amer. 

 Phil. Soc, vol. XXXV, No. 152, 1896. 



