25 
rolled up or partially coiled animals. All 
trilobites, however, have not this power; in¬ 
deed, it seems to be principally confined to 
those only, whose extremities are rounded 
and nearly equal in size. The rolled position 
would afford to the parodoxides and to many 
of the asaphs, but little security against the 
attacks of their enemies, and we rarely if 
ever find them in this attitude. The remark 
of Professor Wahlenberg above cited, though 
illustrated by the specimens now under con- 
sideration, we think of far too general a na¬ 
ture. 
The deep cavity beneath the tail in the 
fragments which we are describing, reaches 
forwards towards the head as far as the ninth 
articulation of the back; in other words, a 
portion of it lies beneath the three last ab¬ 
dominal divisions. It will be recollected that 
the gullar pouch reaches below the fourth 
articulation of the back, and that the whole 
number of divisions in the vertebral column 
in the genus calymene, is twelve; we have 
therefore discovered in these fragments ah 
3 
