50 INVERTEBRATE ANIMALS. 



the Eose of Jericho (Anastatica Hierocliuntia) . 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 

 many thousands. Estimated number of species : 

 recent, 16 ; British, 1. 



H Examples of Asterophyton (Linck) ; Euryale 

 (Lamarck). 



Order ASTEROIDEA. u<TTrip, a star; sISoj, 

 form. 



Ambulacral furrows with four rows of tube-feet ; anus dorsal. 



Group 139.— Genera ASTERACANTHION (Mliller) ; and 

 HELIASTER (Gray). This group includes the com- 

 mon star-fish or cross-fish, found abundantly on the 

 shores of the Mersey. The arms of star-fishes have, on 

 the under side, furrows pierced by rows of openings 

 through which can be extended or retracted locomotive 

 organs called tube-feet. A complicated apparatus (the 

 water-vascular system) fills or empties, and thus pro 

 trudes or withdraws, these tube -feet, or any portion of 

 them, at the will of the animal. Estimated number of 

 species : recent, 50 ; British, 4 ; fossil, 9. Silurian 

 and upwards. In this, as in most groups of the order, 

 the collection is indebted for fine examples to the liberal 

 contributions of Professor Agassiz. 



