28 SVEN LOVEN, ECHINOLOGICA. 



an 1, that is witli an entire plate, in a state of disintegration 

 and transformation, whereas the eolnmns 1 ft, II 6, III a, IV 

 /;, V a each of tliem end witli a H, that is witli the innermost 

 demi-plate of the preceding plate, but more or less augmented 

 and transformed. It is so that at this point a new order sets 

 in. The plates are one by one detaehed, and gradnally trans- 

 formed into scales as in the Cidaris, but in a thoronghly dif- 

 ferent manner. In the Cidaris the auricles arise from the in- 

 terradia and conse([uently the passage downwards of the am- 

 bulacral plates which are all similar, entire and simple, is free, 

 and the mode of transformation the same for them all, every 

 one in its turn being operated npon like the others, precedent 

 and following. In the Asthenosoma on the contrary, not only it 

 belongs to the plates wliich at the tinie are peristomal to support 

 the auricles, but the plates being unequal, every two minute 

 demi-plates are followed by one large entire plate. This subordi- 

 nation of the two plates of the triad is undone in the act of 

 separation and transformation, and every successive plate, en- 

 tire or demi-plate, large or small, invariably and irrespecti- 

 vely of its precedent condition. is brought into the shape and 

 size which conforms to the place it will have to iill in one 

 of the five triangulär buccal areas. At the same time, the 

 steady support of the auricles must be maintained. To this 

 pud, during the whole of the process, the sutures between the 

 ])lates become closer, the connecting fibrous tissues stronger 

 than they were liigher up, and the tirmness of the whole 

 structure is kept up by the moving plates. In the I a, II «, 

 III 6, IV a, V b, the entire plate I, wliich is foremost in the 

 iixed peristome, in parting from it, glides with its external 

 lobe under the base of the auricle, and supports more than 

 the half of its base, the rest being sustained by a now pro- 

 duced lobe of the following demi-plate 2. The entire plate I 

 löses in circumference, and the part of it that bears the pore, 

 in size like one of the demi-plates, separates from it, leaving 

 an indentation. At the same time, in the other column, the 

 corresponding demi-plate 3, which is foremost in the I &, II 

 />, III o, IV h, V w, in approaching the peristome receives on 

 either side an inner, or sometimes even outwardly visible, la- 

 meilar lobe (see woodcut fig. 2 — ö) transverse and rectangnlar, 

 that expands externally beneath the base of the auricular 

 branch, and supports it in common ^^•ith the following entire 



