748 
DE. W. B. CAEPENTEE AND ME. H. B. BEADY ON 
43. The tubular condition of the principal part of the secondary skeleton has been in- 
ferred from the appearances presented by portions of exceptional specimens in which the 
infiltration has least obscured the structure. But in the absence of these, there would 
have been sufficient evidence to be gained from a close comparison with corresponding 
appearances in ParJceria, to demonstrate the general tubularity of the labyrinthic system. 
This character is foreshadowed in a group of Foraminifera of much simpler type. I 
have elsewhere* described the occurrence in Pllijpsoidina (an interesting genus of Fora- 
minifera discovered by Professor Seguenza in the Miocene clays of Sicily) of a line of 
tubular columns, whose only ostensible office is to support a series of chambers which 
otherwise would have but little connexion with each other. There is a strong reason 
why the accessory skeleton which forms so large a proportion of the entire bulk of the 
shell in Loftusia should be built up on a plan that would ensure the greatest strength 
with the least weight. The habit of Foraminifera is to live on the surface of the sand 
or mud at the bottom of the sea, and recent shells taken from a position entirely beneath 
the top of the mud are dead and empty ; — in point of fact the animal dies if it is buried 
in the sand. It is clear from the nature of the limestone matrix, that the floor of the 
sea in which Loftusia lived was a very fine calcareous mud, soft and oozy. Now the 
specific gravity of the material of which the skeleton is built is about 2*7; and sarcode 
itself may be regarded as but little heavier than water ; so that if, as may he supposed, 
the hollow 7 sinuses were occupied by sarcode, it would materially alter the relation between 
the specific gravity of the animal and the element in which it lived ; that is to say, the 
mass comprising the shell and the sarcode would be of much low 7 er specific gravity than 
would be the case were the skeleton solid : — hence the animal would be correspondingly 
better fitted to preserve its natural habitat. It is not certain, however, that the laby- 
rinthic sinuses were occupied by sarcode, or even that the ends projecting into the 
sarcode-cavities were open ; and it is still possible that they may have fulfilled some 
distinct functional purpose. In the absence of evidence on this point, it is needless to 
dwell upon it ; but it is within the range of possibility that the cancellated structure 
may during life have formed a sort of water-system, or perhaps may even have been 
filled in part with air. These are but surmises that have presented themselves during 
the investigation ; but if either condition existed, it would further reduce the general 
specific gravity. 
44. Physical and Chemical Pelations. — The condition of this fossil is very unfavourable 
for the determination of the elementary physical characters of the original organism, 
owing to the completeness of the mineralizing process to which it has been subjected. 
The sand of which the test is formed is entirely Calcareous ; and its identity in chemical 
composition with the mineral substance occupying the sarcode-cavities renders it impos- 
sible to separate or distinguish the two by means of reagents. We learn also from the 
study of the different condition in which specimens of ParJceria have been found, that 
the infiltration of a substance having the same chemical composition as the test has a 
* Annals and Magazine of Natural History, 4 ser. vol. i. p. 333, pi. xiii. 
