CRETACEOUS FOSSILS. 177 



angular and strongly shouldered, the upper surface being' flattened or a little 

 Fig- (i. concave, with usually a slight outward slope from the suture 



to the angle or shoulder, where it meets the vertical outer sur- 

 face nearly at right angles; last or bod3^-volution large, or 

 generally composing about two-thirds the entire bulk and 

 length of the shell; sutui'e well defined by the prominence 

 nnd angularity of the volutions, but not channeled. Sur- 

 f.ico of each turn ornamented by about ten to fifteen rather 

 strong, vertical, or slightly oblique folds, or costje, each 

 of which terminates in a small nodular projection at the 

 shoulder above, so as sometimes to impart a subcoronate 

 tiiio imich bettL-i appearance to the same, while they all become nearly or 

 ligucedou the plate, quite obsolcte below the middle of the body- volution; ver- 

 tical costse crossed by smaller, but quite distinct revolving, raised lines, or 

 small ridges, some four to six of which may be counted on the outer surface 

 of each turn of the spire, and about ten on the body-volution, where they 

 increase in size downward ;* upper flattened surface of the volution generally 

 only marked by the moderately distinct lines of growth seen below; aperture 

 obliquely rhombic -subovate, being higher than Avide, rounded-subrectangular 

 above, and narrowed and more or less angular, Avith a slight sinus or notch, 

 at the connection of the outer and inner lips near the middle below; colu- 

 mella arcuate; inner lip, in mature specimens, rather thick all the way up, 

 but more so below, where it is somewhat reflected and margined by a slight, 

 revolving umbilical furrow, with usually an angular outer margin; outer lij) 

 sharp, prominent near the middle, and retreating below and at the angle of 

 the Avhorls aboA'e. 



Length of the largest specimen seen among hundreds, l.G 5 inches; 

 breadth, 0.00 inch; height of aperture, 0.81 inch; breadth of .same, 0.60 

 inch. 



All of the specimens of this shell first studied, as well as all those for 

 some years after brought in, had the outer lip and lower part of the colu- 

 mella broken away, so that no very clear idea, of the nature of its a])ei-ture 

 and the connection of its outer and inner lips below could be formed from 

 them ; while, in all its characters that could then be determined, it so closely 



*Tbese revolving ridges ;ire re|)re.seiitetl too eoarse in tbe above figure. 

 V2. V M 



