96 



THREE CRUISES OF TIIE " BLAKE. 



other sea-urchins ; they are probably modified pedicellariae. 

 The test of Asthenosoma is of a deep claret-color. Phormo- 

 soma placenta, another of the modern Echinothuriae (Fig-. 360), 

 is grayish, or sometimes of a deep brick-color or a yellowish 

 orange. The coronal plates of both zones, although they appear 

 at first glance similar in structure to those of the regular sea- 

 urchins, yet are frequently split up into four distinct plates, as 

 in the palaeozoic Archeocidaris and the like. 



In a type recalling the Cidaridae and the Diadematidae, Aspi- 

 dodiadema antillarum (Fig. 361), remarkable and interesting 

 pedicellariae are found scattered over the whole of the abac- 

 tinal part of the test. These may be called sheathed pedicel- 

 lariae. The shaft con- 

 sists of a long, slender 

 radiole, distinctly ar- 

 ticulated, surrounded 

 by a huge fleshy 

 sheath, swelling out 

 into three large bags 

 on the sides. (Fig. 

 362.) The sheath 



Fig. 361. — Aspidodiadema antillarum. |. 



Fig. 362. — Aspidodiadema an- 

 tillarum, magnified pedicellaria. 



expands at the extremity into a three-lobed cupuliform tip. 

 These pedicellariae recall the remarkable sheathed secondary 

 spines of Asthenosoma, and form an additional link in the chain 



