160 GENESIS OF THE AKIETID^. 



the original at the Ecole des Mines showed the young of the true Bonnardi to be 

 tuberculated, which is not the case with the young of planaries. This fact was 

 apparently not observed by Oppel, who considered planaries to be identical with 

 the typical Bonnardi It is possible that Conybcari, as figured by Hauer, may 

 belong to this variety. 



Vermiceras ophioides, Hyatt. 



Plate I. Fig. 81-23. Summ. PI. XI. Fig. 25. 



Discoceras ophioides, Hyatt, Bull. Mus. Comp. Zobl., I., No. 5, p. 76. 

 Amm. ophioides, D'Oub., Terr. Jurassique, p. 241, pi. Ixiv. 



Locality. — Semur. 



The young is smooth for one volution and a half. On the third quarter of 

 the second, scattered folds begin, developing into true pilte on the first quarter 

 of the third whorl. During the first half of this whorl, after the keel is devel- 

 oped, the rounded sides of the shell show that the form of the whorl, as well 

 as the immature pike, resemble Cal. laqueum. 



The abdominal sulcations are well defined on the last quarter of the third 

 whorl, and from their well marked character on the early part of this quarter it 

 may be inferred that they begin on the third quarter, where, however, they were 

 not directly observed. For the same reasons, also, I should infer that there are 

 well defined lateral ridges to the sulcations almost immediately after their first 

 appearance on this same third quarter. The very rapid appearance of these 

 characteristics probably prevents a repetition, or only permits a very partial 

 one, of the adult characteristics of any of the species intermediate between Calo- 

 ceras Johmtoni and Ver. Conybeari. In the course of the growth through the second 

 quarter, the sides of the whorls remain rounded and the pila? more or less imma- 

 ture, as in the adults of laqueum and Johnstoni. On the third quarter of this whorl, 

 and simultaneously with the channels, the peculiar genicula? and squared or 

 quadragonal whorl appear, and we find also distinct lateral ridges to the channels, 

 a well defined keel, and what seem to be minute tubercles, but are really only 

 very angular geniculce. 



From this period these characteristics, which render a fragment of the adult 

 whorl identical in its aspect with the adult of Conybeari, are increased and 

 strengthened, but not otherwise changed by growth. 



The sutures, however, though observed in only one specimen, differ somewhat. 

 The lobes and saddles are more pointed and have smoother outlines than in Ver. 

 Conybeari. It is a species which illustrates admirably the law of acceleration in 

 heredity. 



Canavari, in his work on the Lias of Spezia, figures under the name of Ver. 

 (Ariel.) spiratissimum, Plate XX. Fig. 2, a very interesting dwarf, with exceedingly 

 narrow channels and linear sunken keel. This is probably distinct, and the name 

 supraspiralas subsequently given by this author, in his republication of this paper 

 in the third volume of the " Memorie della Carta Geologica d' Italia," to the same 



