No. I.] LARVAL STAGES OF SCHLOENBACHIA. 247 



in the early youth of the shell and continues to increase until 

 the adult stage is reached. The septa of a specimen at diameter 

 18.50 mm. are shown on PI. E, Fig. 5. 



vS. oregonensis grows to a diameter of at least 30 mm., although 

 no perfect specimens of that size were obtained. The measure- 

 ments of an adult at end of the sixth whorl are as follows : 



MM. 



Diameter ........ 22.25^1.00 



Height of the last whorl . .... 9.00 = 0.40 



Height of last whorl from the top of the preceding 7.28 = 0.32 

 Width of last whorl ..... 5.00^0.22 



Involution ....... 1.72 = 0.07 



Width of umbiUcus ..... 7.64 = 0.34 



This species is nearest to Schloenbachia chicoensis Trask, 

 Proc. Calif. Acad. Sci., vol. i, p. 92, PI. II, Fig. i, 1856; and 

 Palaeontol. Calif., vol. i, p. 6^, PL XIII, Fig. 17, and PI. XIV, 

 Fig. 17, to which it was doubtfully referred by Mr. F. M. 

 Anderson.^ 



5. chicoensis, as figured by Gabb, has narrower and more 

 involute whorls than 5. oregonensis, flatter sides, and stronger 

 nodes on the shoulder keels, and also has the shoulder keels 

 nearly as high as that on the abdomen. Through the kindness 

 of Dr. J. C. Merriam, of the University of California, the writer 

 was able to examine a series of Schloenbachia chicoensis, as 

 figured and described by Gabb; the following are the dimen- 

 sions of a typical specimen : 



MM. 



Diameter ......... 24.0 



Height of last whorl ....... 12.0 



Width of umbilicus . 5.0 



The dimensions of a specimen nearing the end of the adoles- 

 cent stage are as follows : 



5. chicoensis (as identified by Gabb), 



MM. 



Diameter. ....... 13.00=1.00 



Height of the last whorl ..... 5.3 = 0.40 



Height of last whorl from the preceding . . 4.3 =: 0.33 



Width of last whorl 3.5=0.26 



Involution ....... 1.0=: 0.07 



Width of umbilicus ...... 4.0 =: 0.30 



"^ Journ. GeoL, vol. iii, No. 4, p. 467. 



