TERTIARY FOSSILS. 49 



prominent, each a little more in advance than the corresponding 

 one above, and connected with it by a faint rib, or rather an un- 

 dulation of the surface ; spire low, whorls five, apical angle a 

 little more acute than the superior slope of the last whorl. Sur- 

 face marked by numerous small revolving ribs, with broad, flat 

 interspaces, in which are usually one or more additional linear 

 ribs, or fine elevated lines, the whole crossed by minute line3 of 

 growth. Aperture broad, canal short. 



Length (about) 1.9 inch; width, 1.4 inch; height of spire from internal angle 

 of mouth, .3 inch. 



From the Miocene at Griswold's, between San Juan and New Idria, Monterey 

 County; Pliocene, "Wiley's, San Fernando Pass, Los Angeles County. 



A very strongly characterized and peculiar species, quite rare. It has never 

 yet been found as recent as the Post-Pliocene. The best preserved specimen yet 

 obtained, was found by Mr. Frank E. Brown, in the rich fossiliferous Pliocene 

 Sandstones of the San Fernando Pass, at the west end of San Gabriel Mountains. 



SINUM, Bolt. 1798. 

 Sigaretus, Lam. 1799. 



S. PLANICOSTUM, U. S. 

 PI. 14, Fig. 6. 



Shell oblique, thin, semiglobose; spire small, somewhat ele- 

 vated; whorls three and a half to four, rapidly increasing in size; 

 suture small but distinct ; body whorl very oblique, ornamented 

 by numerous square revolving ribs with flat interspaces of about 

 equal size; umbilical margin acutely rounded; umbilicus imperfo- 

 rate. The under surface, inside of the margin, not costate, but 

 marked by strong lines of growth. Aperture very large, sub- 

 elliptical, slightly emarginate by the encroachment of the body 

 whorl; outer lip acute, inner lip slightly thickened. 



Length, 1.2 inch ; width, 1.3 inch; greatest diameter of mouth, 1 inch; lesser 

 diameter of mouth, .8 inch. 

 PAL. vol. II. — 8 



