HEINZIID®. 129 
young is involute, smooth, and compressed with a rounded venter as in the 
young of Pulchelliide. Then it has a faint line of ventral tubercles and 
flat venter followed by a true Pulchellian stage with channeled venter 
bordered by single tubercles. In other words, at this age the species is 
like Pulchellia except that the tubercles are not elongated crests. The 
ephebic stage shows the usual terminal double row of tubercles of the 
Heinziide. The conclusion from this evidence is that the Pulchelliidee 
probably arose from Heinzia or some very similar form through the increase 
of compression and involution and from the prolongation of the smooth 
larval stages, the suppression of the preliminary lines of ventral tubercles 
in the young and the tendency in later stages to suppress the second lateral 
lines of tubercles. This inference acquires some support also from the fact 
of the earlier appearance of Heinziidz in the Neocomian. We can in this 
way account for the communal resemblances of these two families in their 
adult forms, costee and sutures, but it must be borne in mind that the evi- 
dence upon which this inference is based is not by any means complete. 
The evidence with regard to the connection and genesis of forms is 
less complete than in the Pulchelliidze, but the following diagram gives the 
apparent relations of the genera so far as the ontogeny at present known 
indicates these: 
Metoicoceras 
Gerhardtia Carstenia 
| 
| 
= | Heinzia 
| 
Cheloniceras 
HEINZIA Sayn. 
Sayn® defines this genus in the following terms: ‘‘Les espéces qui se 
rattachent aux Pulchellia subcaicedi et provincialis sont nettement caractér- 
isées par une ornementation vigoureuse, visible dés les towrs embryonnaires, 
un accroissement en général moins rapide, des sutures le plus souvent trés 
éloignées les unes des autres et remarquables par le grand développement 
en largeur des selles et l’amoindrissement des lobes trés ¢troits et peu 
découpés.” The group described by Sayn under this name is obviously a 
«Amm. du Barrémien du Djebel-Ouach prés Constantine: Ann. Soc. d’ Agriculture de Lyon, 6th 
series, Vol. III, 1890, p. 151. 
MON XLIV—03——9 
