ECHINOIDEA. I. 55 



Tetradactylous pedicellariae have not been observed. Of tridentate pedicellariae three kinds are found, 

 with no transitions between them. The first form resembles that in A. fenestratum, but is finer and 

 more slender (PI. XIII. Fig.22); the head i mm . The second form (PL XIII. Fig. 10), which corresponds 

 to the second form in A. /enestratum , is very large, the head 2""". The blade much involuted; the 

 widened part of the point rather large, coarsely sinuate in the edge. The valves only slightly curved, 

 and accordingly the pedicellaria when shut has a peculiar lengthened appearance. The third, smallest 

 form is very characteristic, with involuted edge and the outer end widened, without large curves in 

 the edge (but with fine serrations) (PI. XIII. Fig. 11). Triphyllous pedicellariae of the same kind as in 

 the other species, only more slender (PL XII. Fig. 29). The stalk of the pedicellariae of the common 

 structure. Spicules as in A. /enestratum, in two well-separated series to the very point. Well-developed 

 sucking disk. — For this species I propose the name of Araeosoma Belli n. sp. 



Asthenosoma pellucidum A. Ag. Of this species, which is easily recognised as well by its 

 whole habitus, as by its light spines with red bands, Agassiz says (Chall. Ech. p. 87): Unfortunately, 

 the largest specimens of Asthenosoma pellucidum are so much smaller than the smallest Asthenosoma 

 coriaceum or the single specimen of Asthenosoma tesselatum, that I am unable so satisfy myself that 

 the present species [Asthenosoma pellucidum) may not be the young of Asthenosoma coriaceum. In the 

 only species of the group of which the Challenger collected a complete series [Phormosoma tenue) 

 there was little difficulty in recognising the young as belonging to the adult». We could scarcely 

 wish to find a more pregnant proof of the difficult)* or impossibility of determining Echinids without 

 taking the pedicellariae into consideration. Asthenosoma pellucidum is so far from being identical 

 with A. coriaceum or tesselatum, that it must form a separate, very well characterized genus, and with 

 regard to the excellent long series of Phormosoma • tenue, there are among the specimens referred to 

 this species by Agassiz at all events two different genera, but no genuine Phormosoma] 



In A. pellucidum three different kinds of pedicellariae are found, viz. globiferous, tridentate, and 

 triphyllous ones. The globiferous pedicellariae are of a quite unique 1 ) form (PL XII. Figs. 8—10, 

 PL XIII. Figs. 20, 24, 25); they cannot be opened as other pedicellariae, the three glandular bags are 

 inclosed in a common skin, and open in the point, each through a separate pore. The valves are 

 situated between the glandular bags; they are simple rods, slightly bisected in the point, a little 

 hollow on the inside, and with a rather strong articular surface below. No apophysis is found, and 

 no muscles seem to pass between the valves, what would not be of much use neither, on account of 

 their being quite wrapped by the common bag of skin; they are far from reaching to the point of the 

 pedicellaria. The tridentate pedicellariae resemble to a high degree the pedicellaria of Ph. tenue 

 figured by Agassiz (Chall. Ech. Pl.XLIL Fig. 7). The construction of the blade, however, is rather 

 different: here only a little developed net of meshes is found, and the apophysis is not prolonged 

 (PL XIV. Fig. 9) , in Ph. tenue there is a rather well developed net of meshes , and the apophysis 

 continues some way into the blade as a conspicuous, serrate crest. Only one form of tridentate pedi- 



•) By a cursory examination one might be inclined to compare them with the Globiferen of Cenlrosh-pliauus longi- 

 spinus described bv Ham ami (184). This, however, cannot be done, at all events not for the present; perhaps the head of 

 these modified globiferous pedicellariae will show a structure recalling the form described here. But of this, I think, we know 

 nothing. The large glands of the stalk in the globiferous pedicellaria in Cenlrostephauus cannot, of course, be compared 

 with the glands in the head of the pedicellaria; of A. pellucidum. 



