NATURAL SCIENCES OF PHILADELPHIA. 145 



rounded, or subangular from the beaks to the narrow anal extremity. Sur- 

 face ornamented by very regular, closely arranged concentric striae, about ten 

 of which may be counted in 0'05 of an inch. (Hinge and interior unknown.) 

 Locality and position. Waterloo, Monroe Co., 111. St. Louis Limestone. 



GASTEROPODA. 

 Genus DENTALIUM, Lin. 1740. 



Dentalium venustum. Shell very slender, and slightly tapering, nearly 

 straight, rather thin ; section circular, surface smooth. 



Length, 0*80 inch ; diameter of larger end, 0-09 inch ; do. at smaller end, 

 0-03 inch. 



It is probable where the surface of this shell is well preserved, very fine 

 striae of growth could be seen by the aid of a lens, but in all of those we have 

 examined, no traces of surface markings of any kind are visible. It seems 

 to be allied to D. antiquum, of Goldfuss, (a Devonian species,) but is propor- 

 tionally thinner, and has a smooth surface. From D. priscum of Munster, it 

 differs in being much more slender and more gradually tapering. We have 

 before us a few fragments of apparently the same species, but of larger size, 

 from Spergen Hill, Ind., where they are associated with the small fossils de- 

 scribed by Prof. Hall from that locality. Prof. H. has described in the Iowa 

 Report, (p. 666,) a larger, more robust, and more curved species, from War- 

 saw, 111., under the name of D. primarium, and gives the Warsaw Limestone 

 as its geological horizon. This, however, is an error, the specimen described 

 by Prof. Hall, belongs to one of us, (A. H. W.), and is from the Keokuk Lime- 

 stone, near Warsaw, Illinois. 



Locality and position. Waterloo, Monroe County, 111. St. Louis Lime- 

 stone. 



Genus STRAPAROLLUS, Montfort, 1810. 



Straparollus similis. Shell very small, sub-discoidal ; spire much depres- 

 sed, volutions four and a half to five, increasing rather gradually in size, hori- 

 zontally flattened above from the suture to a moderately distinct revolving 

 angle near the middle of the upper side, thence a little compressed on the 

 upper outer slope, and rather narrowly rounder over the periphery ; under 

 side of last turn rounded, excepting in the middle, where there is an obtuse, 

 but well denned revolving angle. Umbilicus (measuring across from its mar- 

 ginal angle on the middle of the body whorl,) once and a half the breadth of 

 the las i turn at the aperture, deep, and showing the inner side of all the 

 whorls of the spire ; suture well defined. Aperture subcircular, or a little 

 modified by the succeeding turn, and the flattening on the upper side of the 

 whorls ; lip not oblique. Surface marked by rather obscure lines of 

 growth. 



Height (of a medium sized specimen) 0*18 inch; breadth, 0-31 inch; dia- 

 meter of aperture, 0*08 inch. 



This delicate little shell seems to be almost an exact miniature of our S. 

 planodorsatus, excepting that its spire is a little more elevated, its periphery 

 slightly less regularly rounded, and its umbilicus proportionally smaller. It 

 appears to stand as it were intermediate between that species and our S. um- 

 bilicatus, being more elevated than the first and less than the last. It is cer- 

 tainly not the young of either of these forms, however, since the largest of our 

 specimens never attain more than one-tenth the size of those shells, and yet 

 have the same number of whorls. 



We have before us specimens of a very closely allied form from Spergen 

 Hill, Indiana, which agree exactly in size and form, excepting that the angles 



1861.J u 



