GASTEROPODA. gp, 



MURCHISONIA, de Verneuil and d'Archiac. 



MURCHISONIA DESIDERATA. 

 PLATE XXI, FIGS. 1-3. 



Mtirchisoiiia desiderata, Hall. Descriptions of New Species of Fossils, etc., p. 22. 1861. 



" " " Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 50, pi. 4, fig. 12. 1862. 



Shell elongate, turretiform ; spire somewhat rapidly ascending. Volutions 

 ten or more obtusely angular, flattened on their upper sides, and a little 

 more convex below the spiral band — the lower ones gradually enlarging; 

 the greatest width of the last volution about equal to the height of the 

 two above, and scarcely more ventricose than the preceding one, except 

 towards the aperture. Aperture somewhat elongate ; the columellar lip 

 thickened, and bounded by a well marked callosity. 



Surface marked by distinct concentric striae, which are sometimes raised in 

 fascicles above the general surface of the shell, and bending gently back 

 from the suture reach the spiral band, crossing which they bend forward 

 more abruptly, making a gentle curve to the suture below. The spiral 

 band, at about "three-fifths of the width of the volution below the suture, 

 is simple, flattened or slightly concave, limited by narrow, moderately 

 elevated revolving lines, and marked by the retrally curving striae, 

 which are less prominent upon it and the adjacent parts than near the 

 suture. Suture close. 



The height of five volutions from the mouth upward is nearly two and 

 a quarter inches, and the diameter of the last volution is seven-eighths of an 

 inch. The length of the aperture is about five-eighths of an inch, and the 

 width half an inch, as far as can be determined from the imperfect specimen. 



This species differs conspicuously from either of the two following forms in 

 its proportionally greater length as well as the angularity of the volutions, and 

 the distinct flattening upon their upper side. The suture-line is close, without 

 indication of a groove, and the transverse striae are much less conspicuous 

 than in the other species. 

 12 



