204 The American Geologist. ^p^''- ■'■^'^^• 
considerations as the free mobility of the orthoceratites. But 
as here the fixation of younger individuals and of very differ- 
ent sizes, has been proved, and no fact in the shell structure of 
mature conularias points to other biologic relations, we are not 
only justified but bound to assume also a fixation of the ma- 
ture conularias until the contrary has been demonstrated. 
From the Upper Siluric of Ludlow in England (Lower Lud- 
low beds) I have collected a conularia having a bight of ca 
seventy cm. and hence surely to be considered as fully grown, 
and which, at its pointed end, shows, corresponding to some 
growth-stages figured by Ruedemann, such ;striking phenom- 
ena of bagging in its growth, that I believe I am justified in 
citing it as a direct argument for persisting sessility. 
"d) A transverse cameration of a shell, i.e. in its primitive 
form, an advancing in the shell by means of the formation of 
septa, is found without exception among sessile organisms,"^' 
not only as a typical character of certain groups of life forms, 
as the corals, Chstetidse Sphinctozoa, but also singly in other 
divisions and specially such as, in contrast to their relatives, 
combine attachment with vertical growth, such as Richthofenia 
among the brachiopods, Hippurites among the bivalves, Ver- 
mctus among the gastropods. Such cases as these make cam- 
eration appear as a result of vertical sessility and therefore al- 
low us to infer from such cameration, this sessile mode of life. 
"Lmder the former mode of construing the orthoceratites 
it would have been difficult to cite any probable reason for the 
cameration. On the contrary it would be very strange if just 
that part of the shell had been rendered most fragile by the 
formation of air-chambers, if in swimming it would, as ros- 
trum, have had to possess the greatest power of resistance. 
"Of special moment is the consideration that the formation 
of air-chambers may have largely diminished the body weight 
of the orthoceratites and thereby have counterbalanced tlie 
pressure which otherwise would have rested upon the apex of 
the shell. The latter was thereby largely strained by an up- 
ward pull at the basal chamber and under these circumstances 
the structure could hardly have been more advantage- 
* "The chambered calcareous foraminifers can not here be used for biologic 
comparison, as all chambers are filled with protoplasm and cameration does 
not involve a separation of the animal from the posteriorly situated cham- 
bers." 
