180 PALEONTOLOGY OF NEW JERSEY. 
pose that this feature of the volution left an impressed band on the inside 
of the shell which was subsequently filled, partially or entirely, by the 
deposit of shelly matter on the inside as the shell increased with age and 
size, and that the openings were closed beyond the outer half of the last 
volution. 
PLEUROTREMA SOLARIFORMIS, 0. Sp. 
Plate xx, Figs. 10-14. 
Architectonica Abbottii in part of Gabb: Proc. Acad. Nat. Sci., Phila., 1861, p. 321. 
Shell of more than moderate size, the largest example before me meas- 
uring almost 24 inches in its greatest diameter, by 14 inches in height, and 
is an internal cast with the apical volutions absent. Volutions as preserved 
in this specimen, four in number, and probably one and a half or two 
absent; spire low, conical, the sides forming an angle of about 90°, and 
the volutions flattened on their upper surfaces in a line with the apical 
angle; sutures well marked but not deep, indicating a shell of only mod- 
erate thickness; base of the volutions flattened-convex, leaving the periph- 
eral angle somewhat acutely rounded; the inner part of the base of the 
volution rapidly slopes into the broad, open perspective umbilicus, forming 
a rounded funnel-shaped cavity in which all the volutions are seen, but 
with a very slightly marked suture line separating them. Section of the 
volution rhombically elongate-ovate, the umbilical part being attenuated 
where it joins the preceding volution; along the middle of the outer volu- 
tion there occurs an elevated ridge, which presents the appearance of a 
series of interrupted nodes of an elongate-oval shape, as if the shell had 
been provided with a line of oval openings occupying this position, but 
filling up beyond the outer half of the volution; surface of the shell 
unknown. 
This shell possesses much the appearance of a Solarium, but the over- 
lapping of the outer volution upon the base of those preceding it is a 
marked and distinguishing feature; while the absence of angle bounding 
the umbilicus at once separates it from that genus. The species has been 
confounded in the collection Acad. Nat. Sci., Phila., with Plewrotomaria 
Abbott, from which it differs very decidedly, even more than generically, 
