METOICOCERATID ZX. ALe 
systematically handled with due regard to the collateral evidences, deduci- 
ble from the later stages of development and the obvious relations of the 
adult and even senile stages. Thus in the present case, while the young 
would place this genus entirely outside the pale of the Heinziidee, the 
later neanic and the ephebic stages and old age and sutures show them 
to belong near that group. The peculiar elongated crestlike tubercles, 
the coste, and finally the sutures are of the Pulchellian type. When 
these later stages are allowed their full weight, it is then seen that the 
development shows Metoicoceras to be the descendant of some common form 
from which Carstenia tuberculata and Heinzia provincialis are also descended. 
It is also apparent that this must have been either similar to or identical 
with some species of the coronate genus described here as Cheloniceras. 
The coronate young of Metoicoceras are not reconcilable with the young of 
Heinzia nor any other form of this family, so far as known. The develop- 
ment of Heinzia differs in the suppression of the coronate stage and of the 
sextuberculate stage and the appearance of the approximated lines of tuber- 
cles on the venter of the Heinzian type by a tachygenic mode of develop- 
ment common in this group. The difficulty of reconciling the development 
lies in the fact that the outer rows of tubercles appear later than the ven- 
trals and are not developed, like those of Metoicoceras, from a primitive row 
preceding the ventrals in development. This may be a case of what Cope 
has called retardation of development, but if this is so, the effect is really to 
accelerate the appearance of the Heinzian characteristics of the venter. 
The sutures of the entire groups of Cheloniceratidze and Mantelliceratidee 
are of the same type. The number of lobes and saddles is much more 
limited than in Heinziidze or Pulchelliidee, both on the dorsum and externally. 
The outlines also are excessively complex, with a certain ragged look due 
to their long, subdivided marginals, and also apt to be asymmetrical or trifid 
rather than bifid. There is also a noticeable absence of simple entire sad- 
dles und lobes in the umbilical region. Comparison of the sutures of 
Metoicoceras with those of Heinzia or Pulchellia shows at once resemblances 
that are quite close enough to place swallovi in the same group with Heinzia, 
and the sutures of Metoicoceras are especially close to those of Carstenia? 
tuberculata. The development, being irreconcilable with that of any form 
of Heinziide or Pulchelliidee, shows that the genus can not be placed in 
either of these families without confusing the picture of their systematic 
and genetic relations, so far as now known. 
