PEOTOZOA, CCELEXTERA, AND ECHINODERMA 101 



sentially the same as that of their recent repre- 

 sentatives, except that they often had much longer 

 stems which reached to a length of as much as 50 or 

 even 70 feet ; while the number of arms was frequently 

 limited to ten, which is not the case in any recent 

 species but Pentacrinns naresianus. 



But the deep-sea Echinoids, or sea-urchins, 

 also present some features of particular interest. 

 Professor Agassiz in his report says, ' One of the 

 very first results clearly indicated by the deep-sea 

 dredgings of Count Pourtales and the subsequent 

 investigations of the " Porcupine " expedition was the 

 antique character of the new genera discovered in 

 deep water, and especially their resemblance to 

 the cretaceous genera ; and the study of the " Chal- 

 lenger ' Echinoids has brought this out still more 

 clearly.' 



No fewer than twenty-four genera extend into the 

 abysmal regions ; of these no less than sixteen, nearly 

 all belonging to a new group of Spatangoids, do not 

 live at all in shallow water. 



The most interesting forms among these are the 

 Pourtalesias, a group that has existed since the Chalk. 

 These are heart-shaped urchins with a very peculiar 

 test. ' They all have large coronal plates, recalling 



