No. I.] LARVAL STAGES OF SCHLOENBACHIA. 253 



SchloenbacJiia oregoncnsis remains in this stage about a 

 quarter of a revolution, up to the diameter 3.15 mm., two and 

 seven-eighths whorls ; then without any other change in char- 

 acters the first lateral saddle suddenly becomes indented, as 

 shown on PI, B, Figs. 5 and 6, diameter 3.71 mm., and the pro- 

 jection of the septa on PL D, Fig. 5. This stage does not 

 correspond to any known genus, but the characters have the 

 nature of Lower Triassic genera, and so it may be referred to 

 some unknown form of that age ; it may be provisionally called 

 the Parastyrites stage. At diameter of 4.00 mm. the rounded 

 abdominal shoulders become angular, forming keels. The 

 Parastyrites stage lasts about half a revolution, to near the 

 middle of the fourth whorl. 



Metaneanic. — At diameter 4.5 mm., three and three-eighths 

 whorls, ribs appear suddenly on the sides, faint at first, but 

 rapidly becoming distinct ; this is figured on PI. B, Fig. 7, 

 diameter 5.60 mm., three and seven-eighths whorls. At first 

 the ribs, which branch out from nodes on the umbilical shoul- 

 ders, reach only to the abdominal angles. This stage usually 

 ends with the fourth whorl, at diameter a little over 7 mm., 

 thus lasting about five-eighths of a coil. Near the end of the 

 fourth whorl the septa, which up to this time have persisted in 

 their simple goniatitic character, become slightly digitate, or 

 ammonitic ; this is shown on PL E, Fig. i, diameter 6.00 mm., 

 and Fig. 2, diameter 6.40, a little over four coils. 



Paraneanic. — Near the beginning of the fifth whorl, at 

 diameter between 7 and 8 mm., the ribs begin to form knots 

 on the abdominal keels and the nodes on the umbilical shoul- 

 ders grow stronger. The height of the whorl, in proportion 

 to its width, grows more pronounced, and, instead of a sharp- 

 ened abdomen with a keel, the abdominal shoulders become 

 higher and more angular, and the ventral keel rises little above 

 them. At the same time the septa become more ammonitic, as 

 shown on PL E, Fig. 3, diameter 8 mm., four and one-half 

 whorls, and Fig. 4, diameter 9.20 mm., four and three-quarters 

 whorls. This stage lasts up to a diameter of about 12 mm., 

 five whorls. The ribs and the nodes on the abdominal shouL 

 der keels become gradually stronger, and the whorl grows 



