116 Trans. Acad. Sci. of St. Louis. 



ture into a broad, subcordate disk. The outer lip of the peri- 

 torne with a small, shallow dorsal notch, the inner lip spread- 

 ing over the preceding volution. The dorsum marked by a 

 narrow ridge or carina in the outer half of the last volution, 

 but beyond this the dorsum is flattened. The expanded 

 portion of the outer volution is marked by a few, shallow, 

 inconspicuous wrinkles parallel with the margin; the smaller 

 part of the shell marked by three or four faint revolving ribs 

 on each side, which are entirely obsolete in some specimens. 

 Transverse diameter of the aperture, 42 mm., the longi- 

 tudinal diameter, 33 mm., the height of the shell above the 

 aperture, 12 mm. 



Remarks. In general form this species resembles P. 

 patulus from the Hamilton group of New York, but the aper- 

 ture is more transverse, and the concentric wrinkles are not 

 nearly so strong. 



PORCELLIA CRASSINODA W. & W. 

 PI. V.f.1-2. 



Shell large, discoid, broadly umbilicate, consisting of three 

 or four contiguous or slightly embracing whorls, which rapidly 

 increase in size towards the aperture ; the greatest diameter, 

 83 mm. Volutions subtriangular in transverse section, 

 rapidly increasing in diameter from the ventral to the dorsal 

 side; at the aperture the ventral diameter is 11 mm., and the 

 dorsal, 43 mm., to the tips of the nodes. Lateral surfaces 

 slightly convex; the dorsum gently rounded, marked along the 

 middle by a shallow double groove indicating the position of 

 the slit in the aperture. The dorso-lateral angles ornamented 

 by a single row of distant, strong, obtusely pointed nodes; in 

 the type specimen the nodes on one side are a little in advance 

 of those on the other. Surface marked by fine, revolving and 

 transverse striae which are strongest on the dorsum. On the 

 dorsum the transverse striae slope backward from each side to 

 the central groove where thev meet at an angle of about 120°. 



PORCELLIA OBLIQUINODA White. 



PL V.f. 3. 



Shell of medium size, discoid, broadly umbilicate, consist- 

 ing of four or perhaps more slightly embracing volutions 



