427 
Diagram O.—Section of an octagonal, truncated, cuneiform 
whorl with a concave abdomen in which a gibbous, central, dorsal 
face is formed and the lateral dorsal faces are excessively narrow. 
This may be derived from E by involution and the formation of 
umbilical shoulders and umbilical zones, ex. Apheleceras, Subcly- 
mena. 
Diagram P.—Section of a highly complicated fluted whorl with 
concave abdomen. ‘The venter has become subdivided into a fluted 
central ventral zone, c. v. z., and two fluted lateral ventral zones, 
l. v. z., these having become incorporated with the lateral aspect, 
and the intermediate lateral ventral angles, |. v. g., form the bor- 
ders of what is usually considered as the sides of the whorl. 
The lateral zones lying between the abdominal shoulders, a. g., 
and the umbilical shoulders, u. s., have become subdivided into 
two lateral faces, the outer one, |. f., is a broad flute, and the inner 
one is subdivided into three lateral facets, 1. t., two of them, the 
outer and inner facets, fluted, and one of them, the central one, 
slightly gibbous and ridged. 
The contact furrow has a central dorsal facet, c. d. t., two lateral 
dorsal facets, 1. d. t., and two lateral dorsal faces, 1. d. f., the angle 
between 1. d. t. and cc. d. t. is the tertiary dorsal angle, t. d. g., but 
is not lettered, and the angle between 1. d. f. and 1. d. t. is the dor- 
sal face angle and is also not lettered in this diagram, but these are 
lettered in Diagram Q. The facets are introduced by the subdivis- 
ion of the central dorsal face, which is at first flat, as in L. 
The secondary lateral angle, s. l. g., is developed between the 
flute of the lateral face, 1. f., and the outer facet of the inner lateral 
face that extends from s. 1. g. to u.s. The lateral facets formed 
out of the surface of this face are three in number, marked l. t., 
and the angles between these are the tertiary lateral angles, but are 
not lettered. The angles on the central gibbous lateral facet are 
due to longitudinal striz. 
Diagram Q.—Section of a gerontic whorl of P.. The flutings 
and other ornaments have been obliterated, but the impressed zone 
retains its peculiar characteristics. The more advanced parageron- 
tic substage would approximate to Diagram N, but with more de- 
pressed venter. Coloceras is a phyloparagerontic form, having an 
almost reniform whorl in the neanic and ephebic stages. 
