304 NORTH-CAROLINA GEOLOGICAL SURVEY. 



late head is supported on a jointed foot-stalk. These are 

 called Encrinites. 



These different families have a special geological interest. 

 The last for example, the Encrinite, lived in the earliest pe- 

 riods of the planet, and are known principally in the oldest 

 palaeozoic rocks. In the lower silurian system, beds are of- 

 ten composed mainly of their disarticulated remains. In mod- 

 ern rocks and seas, they are unknown. On the contrary, the 

 star-fishes without pedicels or jointed supports, are known 

 mostly in modern rocks, only two or three species being 

 known in the earlier formations. Now, the sea-urchins, or 

 the globular forms of this class, lived in great numbers in the 

 Mesozoic or Jurassic period. This type or form has come to 

 us, though none of the species of the Mesozoic period live in 

 our present seas. 



I have spoken of the complicated structure of the star-fishes 

 and the provision which has been made for their growth, both 

 of which are worthy of our highest admiration. But nature 

 had not exhausted all her resources when she had provided 

 for their growth and made them the most beautiful objects in 

 the seas. She has in this elaborate structure made their or- 

 namental work subordinate to their instruments of locomotion 

 and reproduction. The flowers which are sculptured upon 

 their integuments form a part of their organs for moving from 

 place to place. These flowers which represent the five petals 

 of a rose, are formed by punctures through the outer envel- 

 ope. Through them the urchin protrudes fleshy suckers or 

 tubes. If, for example, a sea-urchin is placed in a glass filled 

 with sea-water, it is soon seen to protrude a multitude of slen- 

 der fleshy threads, each of which is tipped with a little knob. 

 These soon come in contact with the glass to which the knob 

 adheres, on the principle of an exhausted receiver. By means 

 of this adhering apparatus, it moves itself forward or back- 

 ward. In technical language, the surface from which these 

 fleshy threads protrude, are called ambulacral areas, and the 

 spaces between, interambulacral areas. Nothing can be seen 

 of these threads when the animal is dead. All its soft parts 

 are strictly encased in a box of kard shell substance, which 



