ENGONOCERATID &. 163 
The variation between different specimens in external aspect of the 
casts is not great except in the gerontic stage owing to the greater or less 
development of the nodose costations, but the variations in the sutures are 
such that no two specimens are alike. 
The fourth suture on right side of figured specimen has eleven lobes 
and ten saddles, and is only slightly curved apicad. The arms of the 
ventral lobe are seen cutting deep into the lateral aspect. The inner 
branch of the first lateral saddle is broad, entire, and club-shaped, as are 
all other saddles, except the ninth and tenth, which are bifid. The depth 
and size of the lobe that divides what is here assumed to be the first 
lateral is so like other lobes that it is not always easy to determine whether 
it is a marginal or really the first lateral lobe. The lobes are all clubbed; 
that is, narrow orad and swelling-out apicad, and from first to seventh 
show very faint digitations or indications of from three to four very minute 
incipient marginal lobes, the fifth showing the equal and the remainder the 
unequal numbers of these. 
Specimen 1489a has short lobes and corresponding saddles like the 
above, but narrow outer branches to the first lateral saddles and arms of 
ventral lobe hardly apparent on the lateral aspect. There are eleven lobes 
and ten saddles easily distinguishable, i. e., not overlapping and similar to 
those of the first specimen, but saddles narrower outwardly and broader 
imwardly, and, what is more remarkable, the seventh, ninth, and tenth are 
bifid, the eighth, which is bifid in the first specimen, being entire in this. 
Specimen 1489¢ has such distinct sutures that one hesitates to place it 
in the same species with those marked 1489a and 1489b. The sutures are 
more deeply curved apicad, the outer five saddles and lobes longer and 
narrower, and the inner ones broader and flatter. There are, however, 
eleven lobes and ten saddles visible, as in the others, and the age is about 
the same. The sutures are, however, closely approximated, so that the 
lobes slightly overlap even in the ephebic stage and form columns except 
along the lines of the first to the second. The ninth saddle alone is bifid, 
all others being entire. 
The discoidal aspect of the young in the umbilicus can be plainly 
seen in this specimen. The sutures on the left side have the same general 
character, but differ in details from those of the right side. The outer 
saddles are alike, but the inner ones are narrow and more numerous. 
