424 
PROCEEDINGS OF THE ACADEMY OF 
earina ; the sides of which rise vertically from the whorl and form a feebly 
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. xxiL 2), 
but the band is narrower and more prominent. It closely resembles P. hell- 
cinoides, McCoy, (Synop. Carb; Foss. Irel., pi. 7, f. 6), but is less depressed 
_ and formed of fewer whorls. 
P Pleurotomaria Stella, n. sp.—Shell minute, trochiform, composed of four 
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 strise 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 strise 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 strise 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 strise 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. 
