84 Hr. Th. Moitonsen on some t'cJu'iiofhun'tls 



ft'.iii^lit. Tlie socondavy ppines are provided with a poison- 

 plaiid at llie point. Tlio primary actinal ppines are rather 

 shoit and robust, curved and thorny, ending in a rather hirfje 

 uliite lioof; those ori the actinoslonie are flattened at tiie 

 poirit, without hoot', otherwise thorny as the primary actinal 

 ppines. Tiie seconcUuy spines of the actinal side are likcwistj 

 thorny, but quite small; smooth ones are also found, those 

 near the ambitus provided witii a poison-gland at the point. 

 'Jransverse sections show the primary actinal spines to be 

 almost compact ; iheabactinal ones are hollow as usual. 



The pedicellarife are of three kinds, viz. " tetradactyle/' 

 tridentate, and triphyllous. Tlie tetradactyle pedicellarise 

 (PI. V. figs. 4.-0), which occur only on tiie actinal side, 

 are very interesting, being evidently of a rather primitive 

 form. They are tliree-valved, as isalso the case in A. tessd- 

 latum (de I\Ieijere, ' Siboga' Echinoidea, p. y>D) ; but whereas 

 in the latter species the valves are of the same beautiful 

 highly finished structure as in those of A. fenestratum and 

 coriacfum, tliey are here quite irreguhir, mostly unsymmetri- 

 cf Uy developed ; even the stalk-shaped lower part of tlie bhxde 

 is irregularly constructed. At tiie base of the valves are three 

 rather large glands placed between the valves; they open 

 throufjh a pore at their u] per end. The head of these pedicel- 

 laviae is a little more than 1 mm. long, the whole length of 

 the pedicellaria being c, 3 mm. They do not seem to occur 

 in one of the specimens from the Hamburg Museum ; on the 

 oiler hand, the tridentate pedicellarire are very numerous iti 

 that specimen. 



The tridentate pedicellariaj (PI. V. figs. 8, 9, 18-20) are 

 of one kind only, all intermediate forms uniting the rather 

 diflferenf-looking extreme forms; the large form of triden- 

 tate pedicellaria; found in other species of Ara'osoma is not 

 represented in this species. They are rather variable in size, 

 the largest reaching c. 2 5 mm. (head). In the smaller 

 ones the valves join in their whole length; the edge is 

 strongly sinuate and extremely finely serrate. There is a 

 distinct longitudinal toothed keel in the blade, in continuation 

 of the apophysis, and a nushwork fills out the bottom at 

 the sides of it (PI. \. figs. 18, IS)). In quite small ones 

 the edge is almost straight or with a few indistinct sinuatiotis 

 in the lower part, and the keel is short or wanting. In the 

 larger ones (PI. V. figs. 8, 20) the valves do not join in their 

 wjioie length, but are separate for about the lower third part ; 

 the keel is indistinct. The neck is short, the stalk of tiie 

 usual irregular structure. 



'i'he trifdiyllous pedicellaii* (PI. V. fig. 1 ) are elongate, 



