INVEKTEBRATE ANIMALS. 47 



a Pentacrinite never snapped asunder except at 

 a joint close below one of the whorls of arms 

 which at intervals of about three inches radiate 

 from the stem. If therefore the stem of a 

 living Pentacrinite broke, a whorl was thereby 

 brought in close and even contact with the 

 sea-bottom, to which the arms could cling and 

 again support the animal in an erect position. 



Group 135. — Family COMATULID^. Feather-stars. 

 Although the adult Feather-stars move freely from place 

 to place, in their early condition they are attached by 

 the centre to a fixed stem, in which stage they so 

 much resemble the species of the preceding group, that 

 the larval state of Comatula rosacea received the name of 

 Pentacrinus Europceus. Estimated number of species : 

 recent, 35 ; British, 3 ; fossil, 20. 



Sub-Class ASTEROIDA. Star-Fishes. 



Order OPHIUROIDEA. o<pis, snake; ovpoc, tail; 

 gISoj, form. 



Group 136.— Family OPHIURID^. Part I. Sand-stars. 

 In the Ophiuridse the number of arms is always five ; 

 the arms do not, as in the true Star-fishes, contain 

 extensions of the body cavity, but are simply locomotive 

 appendages. Estimate of species : recent, 80 ; British, 

 2 ; fossil, 9. 



11 Examples of Ophioderma, Ophiura, Ophiolepis, 

 and other genera. 



