INVERTEBRATES. 285 



Genus STRAPAROLLUS, Montfort, 1810. (See page 158.) 

 Straparollus similis, M. and W. 



PL 19, fig, 4 a, 46. 



Straparollus similis, Meek and Worthen, June, 1861. Proceedings Acad. Nat. Sci., 

 Philad., p. 145. 



Shell very small, subdiscoidal ; spire much depressed ; volu- 

 tions four and a half to five, increasing rather gradually in size, 

 horizontally 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 rounded over the periphery; under side of last turn 

 rounded excepting in the middle, where there is an obtuse, but 

 well defined revolving angle; umbilicus (measuring across from 

 its marginal angle on the middle of the body whorl) once and 

 a half the breadth of the last 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 ; diameter 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 somewhat smaller. It appears 

 to stand as it were intermediate between that species and our S. umhilicatus, 

 being more elevated than the first and less than the last. It is certainly not 

 the young of either of these forms, however, since the largest of our specimens 

 never attain more than one tenth the size of these shells, and yet have the same 

 number of whorls. 



We have before us specimens of a very closely allied form from Spurgen Hill, 

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

 whorls are less distinct, and the flattening of the upper side of the whorls is not 

 quite so broad. These, we think, probably belong to the species under consid- 

 eration, as they differ from any of those described by Professor Hall from that 



