424 PROCEEDINGS OF THE ACADEMY OF 



catina ; the sides of which rise vertically from the whorl and form a feebiy 

 bilinear crest a character best seen in specimens with the shell partly worn 

 away ; from the base of the carina the surfaces slope with but little curvature, 

 at an angle of 115 to 120 with each other, and form a well marked sutural 

 angle of about the same value with the contiguous whorl. Apex rather ob- 

 tuse ; angle of sides 67. Aperture roundly quadrangular, produced on the 

 columellar side. Umbilicus remote. 



Height of shell -64(100); width of last whorl -59(92); height of last 

 whorl 53 (83); width of aperture at right angles with columella -29(45); 

 greatest width at an angle of 45 with the columella -42 (66). 



Locality. With P. vadosa. 



Somewhat resembles P. subconica from the Trenton limestone, but the 

 whorls are not so closely crowded being thus more rounded, and forming a 

 much deeper suture. 



Named in honor of Mr. A. D. White, an efficient assistant in the geological 

 survey of the State during 1859 and 1860. 



Pleurotomaria humilis, n. sp. Shell depressed, conical. Band prominent, 

 revolving close to the linear suture in the upper whorls, central on the body 

 whorl ; surface of shell above and below the band but slightly convex on the 

 body whorl, flat on the spire, and making a peripheral angle of 61. Incli- 

 nation of sides 109. Umbilicus small, and apparently perforate. 



Approximate measurements of an imperfect specimen : height -52 (100) ; 

 with -67 (129) ; height of last whorl -46 (88); width of umbilicus -09. 



Locality. With P. vadosa. 



Has the general form of P. crenato-striata, Sandb., (Verstein. Taf. xxii. 2), 

 but the band is narrower and more prominent. It closely resembles P. heii- 

 cinoides, McCoy, (Synop. Carb. Foss. Irel., pi. 7, f. 6), but is less depressed 

 and formed of fewer whorls. 



Pleurotomaria Stella, n. sp. Shell minute, trochiform, composed of for.! 

 and a half whorls closely appressed, and forming an apical angle of about 90. 

 Suture linear, inconspicuous the flat sides of the whorls all lying in the same 

 plane. Body whorl regularly rounded, marked by a raised bilinear band sit- 

 uated a little above the peripheral line, and on the whorls of the spire nearly 

 concealed. The body whorl is ornamented by a line of minute tubercles run- 

 ning close to the suture, and occupying a feeble revolving ridge. No indica- 

 tions can be seen of transverse striae connected with the tubercles. Aperture 

 subcircular, with the columellar lip reflected over the umbilicus. Some sharp 

 irregular incremental lines rise from the umbilical depression, and extend 

 across the body of the shell. 



Height -16 (100) ; width -20 (125) ; height of body whorl -14 (88) ; height 

 of aperture .09 (56) ; width of band at aperture -02 (12) ; number of tuber- 

 cles in one-tenth of an inch, 12. 



Locality. -N. W. \, N. W. {, Sec. 4. Jefferson, Hillsdale county. 



Pleurotomaria exigua, n. sp. Shell very small, depressed-turbinate, con- 

 sisting of three and a half rapidly enlarging convex whorls but slightly ap- 

 pressed and forming a deep suture, with an apical angle of about 87 ,=> . Base 

 of shell convex, descending into a broad, deep umbilicus, from which rises a 

 set of sharp transverse striae crossing the whorl at right angles, but slightly 

 bent backwards on reaching the band, which is broad and situated a little 

 above the peripheral zone, and marked by incremental lines ; above the band 

 similar striae describe an anteally convex curve to the suture. Aperture cir- 

 cular. 



Height of shell -17 (100) ; diameter -18 (106) ; height of last whorl -14 (82) : 

 width of band -02 (12) ; number of transverse striae in one-tenth of an inch 

 counted near the aperture above the band is 24. 



Locality. N. W. \, N. W. , Sec. 4, Jefferson, Hillsdale county. 



[Sept. 



