THE NAUTILUS. 123 



versely diagonal lamella, the anterior end of which is lower than the 

 posterior, which is slightly bent upwards ; above the anterior extrem- 

 ity of this fold is the third palatal fold, a short, slightly oblique 

 lamella, the posterior end of which is slightly curved backwards and 

 slopes more gradually to its termination than the anterior extremity; 

 above this and at its posterior extremity is a short, transverse denti- 

 cle, which lies immediately below the superior arch of the whorl. 



Alt. 3, greater diam. 7-^, lesser diam. 6 mm. Types (No. 2998 

 coll. Walker) from Hamtramck, Wayne Co., Mich. Also from 

 Kent and Monroe counties, Mich.; Muscatine, la.; Knox county, 

 Vincennesand Brownston, Ind. 



This very distinct species was first seen in 1878, when specimens 

 from Muscatine, la., were received from Prof. F. M. Witter, labelled 

 S. wheatleyi Lea, on the authority of the late Dr. Jas. Lewis. Sub- 

 sequently, when the species were detected in Michigan, in reliance 

 on this identification it was so listed in the two papers cited above. 

 The recent receipt of the true S. wheatleyi from Princeton and Boli- 

 gee, Alabama, collected by H. H. Smith and A. A. Hinkley, has 

 shown that the reference of this form to that species was erroneous. 



Although occupying an intermediate position between the well- 

 known S. armigera and S. wheatleyi, crassilabris, is quite distinct from 

 either. In external appearance, compared with armigera (Fig. 1-3), 

 it is smaller and more compactly coiled and higher in proportion to its 

 width, the umbilicus is smaller and deeper, and the angulation of 

 base of the whorl around the umbilicus more pronounced. In armi- 

 gera, the whorls are more regularly rounded and the aperture lacks 

 the crest behind the lip, and is not at all contracted, the thickening 

 within the lip is very slight and does not sensibly diminish its calibre. 

 In wheatleyi (Fig. 7—9) the distinctive features of crassilabris are 

 all intensified. The apical whorls are more depressed, the body- 

 whorl is obtusely angulated above and sharply carinated around the 

 umbilicus, which is funicular, the inner whorls scarcely, if at all, ob- 

 truding beyond the curve of the body-whorl ; the aperture is more 

 oblique and more contracted in front of the crest, which is more 

 prominent. The inner ridge of callus is less developed and lacks 

 the regular concave slope to the edge of lip characteristic of crassi- 

 labris. 



As recently stated by Pilsbry and Ferriss (Proc. A. N. S. P., 

 1906, p. 166) in regard to S. armigera and wheatleyi, the arrange- 



