COILOPOCERATID #. 93 
lateral. They are bitid and about twice as long as the third, the arms and 
sides being cut up by marginals. The remaining lobes are narrow as 
compared with the saddles, and irregularly denticulated. I could not tell 
whether they were of the trifid or bifid type, or both mixed. There were 
eight lobes, the line of involution being occupied by a saddle. 
The venter is capped by a hollow keel, as in novimexicanum, and in this 
species there is the plug, the dark layer, and an inner-shell layer, upon 
which the ventral saddles and lobes abut. 
The sutures are more like those of novimexicanum than any other 
species, and I at first considered this to be the young of that species; but the 
difference im these and in the external characters at the same age are far too 
marked. 
The saddles and lobes are all shorter than in novimexicanum and 
overlap a trifle only from the fourth lateral to the umbilicus. They are 
also much less complicated in outline or less cut into by marginal lobes, and 
less distinctly phylliform. 
The young in section, so far as seen, showed the same general 
development as in Sphenodiscus, but the division of the primitive first laterals 
took place early in the neanic stage. 
The figures (PI. X, figs. 10-21) give the stages as far as these could 
be studied. The protoconch is stout and slightly scaphitoid or irregular in 
shape, like many other Cretaceous forms The second suture had a minute 
siphonal saddle that was distinctly seen by a side light. Fig. 11 shows 
the deepening of the antisiphonal and the beginning of the two first dorsal 
saddles on the first quarter of the second volution. Fig. lla shows the 
lengthening of the antisiphonal, the incoming of two saddles and the 
beginning of a third on the dorsum, the incipient stages of division of 
the primitive second lateral into four saddles of the auxiliary system and 
the arising of the second lateral saddle on the inner side of the primitive 
first lateral saddle. Fig. 12 shows the progressive lengthening of the 
antisiphonal, the presence of a third pair of fully developed saddles on the 
dorsum, the division of the primitive second lateral into four, the definite 
separation of the second lateral saddle, and the incipient stage of the great 
inner branch of the first lateral saddle; also the first appearance of the 
smaller marginals on the outer side of the base of the same 
