8-4 Dr. Til. Moitensen on some EchinolhnriJs 



ptiai^lit. The secondary spines are provided with a poison- 

 gland at the point. The primary actinal spines are rather 

 short and robust, curved and thorny, ending in a rather large 

 white hoof; those on the actinostome are flattened at the 

 point, without hoof, otherwise thorny as the primary actinal 

 spines. The secondary spines of the actinal side are likewise 

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

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

 Transverse sections show the primary actinal spines to be 

 almost compact ; the abactinal ones are hollow as usual. 



The pedicellariaj are of three kinds, viz. " tetradactyle," 

 tridentate, and triphyllous. The tetradactyle pedicellarioe 

 (PI. V. figs. 4-6), which occur only on the actinal side, 

 are very interesting, being evidently of a rather primitive 

 form. They are three-valved, as is also the case in A. tessd- 

 latum (de Meijere, ' Siboga ' Echinoidea, p. H5) ; but whereas 

 in the latter species tlie valves are of the same beautiful 

 higldy finished structure as in those of A, fenestratum and 

 coriaceiim, they are .here quite irregular, mostly unsymmetri- 

 Ccilly developed ; even the stalk-shaped lower part of the blade 

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

 rather large glands placed between the valves; they open 

 llirough a jDore at their u| per end. The head of these pedicel- 

 larise 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 

 other hand, the tridentate pedicellarias are very numerous in 

 that specimen. 



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

 of one kind only, all intermediate forms uniting the rather 

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

 tate pedicellarice found in other species of Arceosoma 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 

 etrongly sinuate and extremely finely serrate. There is a 

 distinct longitudinal toothed keel in the blade, in continuation 

 of the apophysis, and a mesh work fills out the bottom at 

 the sides of it (PI. V. figs. 18, ID). In quite small ones 

 the edge is almost straight or with a few indistinct sinuations 

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

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

 whole length, but arc separate for about the lower third part ; 

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

 usual irregular structure. 



The triphyllous pedicellaiiae (PI. V. fig. 7) are elongate. 



