48 INVERTEBRATE ANIMALS. 



Group 137.— Family OPHIURIDiE. Part II. Brittle -stars. 

 The Brittle-stars are much more active than the Sand- 

 stars, and have a tendency to break themselves up into 

 little pieces when captured. They die instantaneously 

 when placed in fresh water. The Oph'mridce inhabit 

 almost all seas, and are found occasionally at great 

 depths. Estimated number of species : recent, 65 ; 

 British, 11 ; fossil, 11. Silurian and upwards. The 

 total number of species of Ophiuridae, in a list by 

 Theodore Lyman, of Harvard College, U. S., is 164. 



^ Examples of Ophiocoma, Ophiothrix, Ophiacan- 

 tha, Ophiomyxa, and other genera. 



Group 138.— Family ASTEROPHYDE^ (Dujardin). This 

 group includes species with arms varying from perfectly 

 simple stems to the highly branched appendages of 

 Asterophyton, one species of which, known as the 

 Shetland Argus, when curled up somewhat resembles 

 the Rose of Jericho {Anastatica Hierochuntia). In 

 moving, the Asterophyton lifts itself along on tiptoe, 

 resting on the extreme ends of the branches, which 

 thus form a kind of cage. The branches divide dicho- 

 tomously, beginning with the 5 arms ; these, by 

 division, produce 10, and these again 20, and so on. 

 In a New England specimen, mentioned by A. 

 Agassiz, the terminal branchlets were computed at no 

 less than 81,920. Estimated number of species : 

 recent, 16 British, 1. 



IT Examples of Asterophyton (Linck) ; Euryale 

 (Lamarck). 



