Terms in Crinoid Morphology. 61 
being represented by “ Ax ” instead of “ax,” and by the use 
of Arabic instead of Roman numerals. 
We are now in a position to express in the formule the 
number of brachials in any series. To say that the Quartaxil 
is the fifth ossicle of its series is obviously the same thing as 
saying that there are five quartibrachs; while tosay that the 
third mainaxil (or Tetraxil) is the fourth ossicle of its series 
is obviously the same thing as saying that there are four 
tetrastichals. These facts may be expressed symbolically 
thus—IV ax;, and 3 Ax,; which symbols come to mean just 
the same as IV Br-5 and 4St-4, or as IV Br;=I1V ax, and 
4St,=3 Ax. Applying this method to the formule we get 
such results as these :— 
Thenarocrinus callipygus. 
hax: Eh AX (yy « Max LV —Vili ax 
which being interpreted is, Primibrachs 8, Secundibrachs 4 
asa rule, Tertiobrachs from 4 to 10, Quartibrachs, Quinti- 
brachs, Sextibrachs, Septimibrachs, and Octavibrachs from 6 
to 18, number of finials uncertain. It also conveys the infor- 
mation that the arms branch eight times, that they are non- 
pinnulate, and that none of the brachials enter into the 
dorsal cup. 
6-18 Sy 
Botryocrinus pinnulatus. 
Tax,.2 St-35+, 
which indicates that there are four primibrachs, which are 
free, that there are two arms to each ray, which do not branch 
again but which bear pinnules, and that the number of ossicles 
in each of these arms is uncertain, but exceeded 35. 
Botryocrinus decadactylus. 
Tax, ,- (IL ax, & II Br). 2 8t. 
The facts expressed by this are somewhat more compli- 
cated. Primibrachs are usually 3 or 4, but may be more or 
less; they are free. It is clear from the symbol 2 St that 
the arm bifurcates on the primaxil ; but the signs in brackets 
that precede 2 St show that the earlier ossicles of this distichal 
series do not all bear pinnules, there being first a simple 
secundibrach, then a secundibrach bearing either a pinnule or 
armlet, then a simple ossicle which is morphologically a 
tertiobrach, and then the series of pinnuliferous distichals of 
which the number is uncertain. 
