844 A. Hyati—Biologidil Relatians of the Jurassic Ammonites. 
quincuncial and imbricate (as if the former were not the typical 
case of the latter when the parts are five), and so have had to 
devise something else to answer to imbricate. Alphonse De 
Candolle (in his Introd. Bot., i, 154, written before phyllotaxy 
was well understood), after relegating imbricative to the cate- 
gory of a crowd of verticils, and remarking that the quin- 
cuncial is sometimes confounded with the imbricate, adds: 
some confound also under this latter name the case in which 
there is one exterior piece, one interior, and three covered at 
one margin but free at the other. I know not where this 
_ began; but its latest reproduction is in Le Maout and De- 
eaisne’s Traité Général, and in the English translation of it. 
In the diagram the pieces are numbered directly round the 
circle from 1 to 5, the fifth coming next the first: “so they 
thus complete one turn of a spiral,”—which shows that Le 
Maout had vague ideas of phyllotaxy, of which he seems to 
have invented a new (3) order. Moreover this is essentially 
identical with the cochlear estivation of the same work (not of 
Lindley); and Eichler, in his Bliithendiagramme, adopts this 
name (unsuitable though it be), for this particuliar arrangement, 
whatever be the position of the enclosed or enclosing petal. 
glance shows that this supposed “true imbricate sestivation” 1s 
a slight and not very uncommon deviation (by the displace: 
ment of what should be the interior margin of one of the petals 
during growth) of the mode II, variously termed obvolute, con- 
volute, or contorted wstivation. But it is so intermediate be- 
tween this and the quincuncially imbricate as perhaps to justify 
Brown in applying the name imbricate generically to all the 
general. 
Art. XLV.—Abstract of a Memoir on the “ Biological Relations 
of the Jurassic Ammonites ;’ by Professor A. HYAtT.* 
THE speaker traced the history of the evolution of the order 
of Ammonoids, showing that the characteristics of the first three 
stages of the embryo were inherited from a very early perio 
These were first, the sac-like shell of the embryo containing the 
equally sac-like beginning of the siphon,—prosiphon as It has 
since been called by M. Munier-Chalmas; second, the begi- 
S eR oe 5 : : vol. xvii, 
: De aca eee Natural History, 
