CHAP. 1X. ] THE DEEP-SEA FAUNA. 447 
the Jurassic period, when they were represented by 
many fine species of the genera Apiocrinus and 
Millericrinus. The chalk genus Bourguelticrinus 
shows many symptoms of degeneracy. The head 
is small, and the arms are small and short. The 
arm-joints are so minute that it is scarcely possible 
to make up a series from the fragments scattered 
through the chalk in the neighbourhood of a cluster 
of heads. The stem, on the other hand, is dispro- 
portionately large and long, and one is led to suspect 
that the animal was nourished chiefly by the general 
surface absorption of organic matter, and that the 
head and special assimilative organs were principally 
concerned in the function of reproduction.  Jthizo- 
crinus loffotensis, M. Sars (Fig. 72), was discovered 
in the year 1864, at a depth of about 300 fathoms, 
off the Loffoten islands, by G. O. Sars, a son of the 
celebrated Professor of Natural History in the Uni- 
versity of Christiania, by whom it was described in 
the year 1868. It is obviously a form of the Apio- 
erinidee still more degraded than Bourguetticrinus, 
which it closely resembles. The stem is long and 
of considerable thickness in proportion to the size 
of the head. The joints of the stem are individually 
long and dice-box shaped, and between the joints 
spaces are left on either side of the stem alternately, 
as in Bourguetticrinus and in the pentacrinoid of 
Antedon, for the insertion of fascicles of contractile 
fibres. Towards the base of the stem branches 
spring from the upper part of the joints; and these, 
each composed of a succession of gradually diminish- 
ing joints, divide and re-divide into a bunch of 
fibres, which frequently expand at the ends into thin 
