300 



PHYLUM ECHINODERMATA. 



FIG. 208. Pentacrinus wyviUe-thomsoni Jeffreys, nat.-size 

 (from Wyville Thomson). 



Fam. 3. Bourgueti- 

 crinidae. Calyx small, 

 consisting of 5 basals, 5 

 radials, and sometimes 

 2x5 primibrachs. Calyx 

 cover membranous with 

 5 orals. Ambulacra 

 with covering plates, but 

 without side plates. 

 Stem with branching 

 root. Jurassic to pre- 

 sent time. Bourgueti- 

 crinus d'Orb, Tertiaries ; 

 Rhizocrinus Sars (Cono- 

 crinus d'Orb.), the arms 

 are very variable in 

 number, out of 75 speci- 

 mens examined by Sars, 

 15 had 4 arms, 43 had 

 5, 15 had 6, 2 had 7 (W. 

 Thomson, Depths of the 

 Sea, p. 448) ; Eocene, 

 and present time at 

 great depths ; Meso- 

 c.rinus H. Carp., Cretace- 

 ous ; Baihycrinus W. 

 Thorns. (Fig. 206) recent 

 at great depths, 10 arms, 

 orals aborted. 



Rhizocrinus (Fig. 207) 

 was discovered by G. O. 

 Sars among the Lofoten 

 Islands in 1864. The 

 interest of this discovery 

 led to the expedition of 

 H.M.S. Lightning in 

 1868, of the Porcupine 

 1869-70, when Bathy- 

 crinus was discovered, 

 and later of the Chal- 

 lenger in 1874. 



Fam. 4. Saecocomidae. 

 Calyx small, hemispheri- 

 cal, non-pedunculate. 5 

 thin radials, elevated 

 into ridges. Arms 5x2, 

 arm plates cylindrical 

 with wing-like expan- 

 sions, Upper Jurassic. 

 Saccocoma Ag. 



Fam. 5. Pentacrinidae. 

 Calyx small, consisting 

 of 5 basals, 5 radials, 



