j 3 PA LA70NT0L 00 Y OF NEW YOU A . 



giving expresssion to this class of fossils as they occur in these rocks. Since, 

 however, this is the ordinary if not universal condition of some of the species, 

 we have no other means of illustrating the fauna, nor the student of designating 

 the species than from the casts; and by those alone are the formations 

 sometimes to be distinguished * 



The following species of Loxonema, illustrated upon plate 28, appear to 

 be quite distinct from those described in the preceding pages. 



Loxonema rectistriatum, n. sp. 



PLATE XXVIII, FIG. 9. 



Shell elongate terete. Volutions probably twelve or more in number, moder- 

 ately convex, very gradually increasing in size, the last one being scarcely 

 more ventricose than the preceding ; each volution is distinctly contracted 

 a little- below the close suture, and then expanding gives the greatest 

 convexity near the lower third. Suture-line close. Aperture ovate, with 

 the columella extending below. 



Surface marked by slender, gently curving longitudinal striaa, which bend 

 backward from the suture to the bottom of the constriction, and then 

 continue to the base of the volution — those of the last one curving gently 

 forward to the columellar lip. The spaces between the striae are from 

 once and a half to twice the width of the ridges. 



This species may be distinguished from any other described in this volume 

 by the finer longitudinal striae, which are scarcely curved on the body of the 

 volution, and also by the constriction of each volution just below the suture- 

 line. The striae are stronger on the upper volutions, gradually becoming finer 

 and less prominent on the lower ones, though continuing distinct throughout. 

 The specimen figured, which preserves about eight of the lower volutions, 

 measures a little more than one inch in length. 



* Wh«re the sjiecimens occur in the condition of casta only, the difficulties of determining the genera 

 Loxosbma and MrRCiimoMA are often insurmountable ; and among Platyckrah, Cyclonbma, Plkihotomaria 

 and CalloKkma, the forms are so nearly alike that the casts offer few charactem for genenc determination. 



