NUMBER OF SPECIES. 
379 
Eighty-eight species of Belemnites have al- 
^t;ady been discovered ;* and the vast numerical 
■'inioiint to which individuals of these species 
Were extended, is proved by the myriads of their 
fossil remains that fill the Oolitic and Cretaceous 
formations. When we recollect that throughout 
^oth these great formations, the still more nume- 
rous extinct family of Ammonites is co-extensive 
^dh the Belemnites ; and that each species of 
"^luinonite exhibits also contrivances, more com- 
plex and perfect than those retained in the few 
of the Belemnite, beyond the base of its hollow calcareous 
I'One, (Pi_ 44'^ pjg_ 7^ xhis horny sheath of the Be- 
fiWnite was probably formed by the prolongation of the horny 
>^1111® which were interposed between its successive cones of 
bro-calcerons matter. 
The chambered alveolus of the Belemnite is represented by 
de congeries of thin transverse plates, (PI. 44, Fig. 4, b.) 
' '‘oh occupy the interior of the shallow cup of Sepiostaire, 
® ■) : these plates are composed of horny matter, penetrated 
"'ith carbonate of lime. 
'I he hollow spaces between them, (Fig. 5 , b, b',), which are 
"early a hundred in number in the full grown animal, act as air 
" 'ambers to make the entire shell permanently lighter than 
"jater ; but there is no sipbuncle to vary the specific gravity of this 
^ " ; and the thin chambers between its transverse plates are 
titT minute columnar, and sinuous par- 
"s, planted at right angles to the plates, and giving them 
^"Pport. (Fig. 6', 6”, 6"'). ' 
'" absence of a sipbuncle renders the Sepiostaire an organ of 
0 simple structure, and of lower office, than the more com- 
shell of Belemnite. 
B > index to M. Brochant de V'illiers’ Translation of De. la 
" s Manual of Geology). 
