(l) 58 Palicontologia Si'nica Scr. B 



between. Thus viewed, the filling of the shell, whether with air-chamber-enclosing 

 septa, with successive close-set endosheaths, or with solid lime, punctuated at intervals 

 by endosheaths, is a matter of the relativity in the intensity of the lime-depositing 

 ability, between the edge of the mantle and the entire surface. 



^^iewed in this light, the structure of the Holochoanites appears to be the natural 

 result of a sedentary life-habit, or perhaps the tendency towards rapid lime deposition all 

 over the mantle-surface, forced the animal to assume a benthonic mode of life, which 

 eventually must have been sedentary to all intents and purposes. That the Holochoani- 

 tes, or the majority of them, led such a life on the bottom of the sea, is abundantly 

 attested by their structure (especially the ventral flattening), and by their general mode 

 of occurrence in the rocks {vide position of Chihlioceras as discussed on p. 48). 



The building of caniorfo in the Holochoanites must on this view be regarded as a 

 neMly acquired character, those structures being analogous to, but not homologous with, 

 the camenTe of the Orthochoanites (Ortliocems etc). They must represent an expansion and 

 reflexion of the mantle-edge, resulting in the addition of a new shell outside of the shell 

 proper (the so-called siphuncular shell or wall, or the endosipholining), and we thus have 

 tlie original shell enclosed by a secondary one, analogous to, but of course not strictly 

 homologous with, the so-called shell of the Argonauta, tlie guard of belemnites, and the 

 "apical cap" of Orthoceras truncatntn. These new shells would thus form sub-annular 

 structures of triangular, and later, more or less rhombic sections, like an automobile tire 

 or a life preserver compressed into a triangular or rhombic section ; but in most cases not 

 extending entirely around the original shell, because this rested upon the bottom. The 

 first of those veritable life-preservers, which probably aided the animal in keeping its oral 

 end from sinking into the mud of the sea-bottom, formed the new shell by its outer or 

 exposed side, and its first '' camera ", by its upper and inner side, which latter lay next 

 to the original (inner) shell, and formed the so-called siphonal funnel of the cameras. 



This interpretation meets with the difiiculty of conceiving the modus operandi of 

 the Ijuilding of such an outer, closed air chamber around the shell. Especially would it 

 seem hard to explain the manner of building of the inner wall of this chamber, i. e. the 

 so-called siphonal funnel of the camerse, that part next to the inner shell or endosipholin- 

 ing. This difficulty may perhaps he obviated by assuming that the animal built at first a 

 sub-annular or semi-lunar troiigh around the margin of the shell, by a compound reflexed 

 portion of the mantle-edge as shown in the following sketches (Figs. 17 and 18). Such a 

 structure is entirely analogues to the lateral alveoli of the final endosheath of Chihlioceras. 

 (Plate II, figs. 13 a, b., also text-figs. 4, 5, 7, 10, 13 pp. 45-49). The second outer 

 trough, built in this manner, would then c'ose the preceding one and convert it into an 



