CHARACTERISTIC DEEP-SEA TYPES. SEA-URCHINS. 101 



Perhaps the most interesting group of sea-urchins discovered 

 by the late deep-sea explorations are the Pourtalesiae. The first 

 Pourtalesia was dredged by Pourtales in the Straits of Florida, 

 a single specimen only (Fig. 373), but sufficiently perfect to 

 enable me to make an examination of this extraordinary type, so 

 different at first glance from any sea-urchin previously known. 



Fig. 37J5. 



Pourtalesia miranda. 



Fig. 374. 



The study of that species, Pourtalesia miranda (Fig. 374), 

 showed affinities to a singular family of urchins described from 

 the chalk, as well as extended relationship to types considered as 

 long extinct. The Ananchytidse, to which the Pourtalesiae are 

 allied, are perhaps the most typical cretaceous sea-urchins. 

 They all have large coronal plates, recalling the Echini, with a 

 disconnected apical system characteristic of many cainozoic spa- 

 tangoids ; they have a sunken anal system, some of them a most 

 remarkable anal beak, and a very striking pouch, in which the 

 mouth is placed. They possess rudimentary fascicles, and their 



Fig. 375. 



Fig. 376. Profile of Fig. 375. 



tuberculation allies them to the clypeastroids. Another species 

 of the same group, which has a wide geographical distribution, 

 is Urechinus naresianus (Figs. 375, 376), which seems to be as 

 common in some parts of the Pacific as in the Atlantic. 



