494. UM. Foord & Crick—Shell-muscles of Ceelonautilus, ete. 
tendency is particularly strong, and usually leads to the construction 
of crystals built up of innumerable layers, different in chemical 
constitution and often so fine as to require the microscope for their 
detection. Since olivine represents an isomorphous mixture of Mg? 
SiO* and Fe® SiO*, it should be equally liable to this structure, 
and the poverty of observations on the point seems all the more 
remarkable. 
If the outline of the inner zone be studied, decided evidence of 
its corrosion through the fluid magma, previous to the deposition 
of the outer shell, will be observed. This alone is proof of the two 
zones representing different periods of growth. The corroded form 
of this inner zone reminds us of the analogy existing between a 
erystal and an organism in manner of growth. The influence of the 
environment has already been referred to; but the regeneration of 
lost or injured parts? is also common to both. M. L. Pasteur has 
particularly studied this property in crystals. He refers to the 
process as follows: “Quand un cristal a été brisé sur l’une quel- 
conque de ses parties et qu’on le replace dans son eau mére, en méme 
temps quil s’agrandit dans tous les sens par un depdt de particules 
cristallines, un travail trés-actif a lieu sur la partie brisée ou deformée, 
et en quelques heures il a satisfait non-seulement 4 la régularité du 
travail général mais au rétablissement de la régularité dans la partie 
mutilees. 2.2 La partie endommagée reprend peu & peu sa forme 
primitive, mais la travail de reformation des tissus est en cet endroit 
bien plus actif que dans les conditions normales ordinaires.” * 
Applying these observations to the case under consideration, we 
conclude that, corrosion having ceased and the constructive process 
having recommenced, growth was more rapid at the corroded than 
at the uninjured part of the crystal. Consequent upon this special 
activity, regularity of form was re-established, and, ‘‘ regeneration ” 
having thus occurred, constant accretion completed the crystal. 
14, Hume Srreer, Duswin. 
VI.—On tHe Muscunar Impressions or C@LonavUTILus ? CARINIFERUS> 
J. DE C. SowERBY, SP., COMPARED WITH THOSE OF THE RECENT 
NavrtiLus. 
By Artuur H. Foorp, F.G.S., and G. C. Crick, F.G.S. 
Te examining the remarkably fine series of examples of Ccelo- 
nautilus cariniferus, mostly from the Carboniferous Limestone of 
Treland, contained in the Geological Collections of the British 
1 Ger. Reproduktion verletzter Theile. 
2 « Etudes sur les modes d’accroisement des cristaux, etc.’? Compt. rend. tome 43, 
1856, p. 795; see also, F. Scharff, ‘‘ Ueber die ausheilung verstiimmelter oder im 
Wachsen verhindert gewesener Krystalle, etc.,’” Pogg. Ann. vol. 109, 1860, p. 529 ; 
W. Ostwald, Lehrbuch d. allg. Chemie, Leipzig, 1885, Bd. i. p. 738; according 
to Scharff (l.c.) Jordan made an observation similar to Pasteur’s as far back as 1842 
(in Miller’s Archiv.). y 
3 This name from koiAov hollow (referring to the umbilicus), and Nawtzlus, is 
proposed by one of us in substitution for Zrematodiscus, Meek and Worthen, which 
