chap, ix.] THE BEEP-SEA FAUNA. 447 



the Jurassic period, when they were represented by 

 many fine species of the genera Apiocrinus and 

 JIUlerlcrinus. The chalk genus Bourgiietticriniis 

 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. Rhizo- 

 crinus loffotensis, M. Sars (Fig. 72), was discovered 

 in the year 1864, at a depth of about 300 fathoms, 

 off the Loffoten islands, by Gr. 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 186S. It is obviously a form of the Apio- 

 crinidse still more degraded than Bourgiietticriniis, 

 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 Boiirguetticrinus 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 



