. Echinoidea of the Swedish South Polar Expedition . The apical system, which is somewhat sunken along the median line, is very interesting, being of a quite primitive structure (PI. XVII Fig. 1). All the four genital plates are distinct, each with a genital pore covered by a long genital pa- pilla; they join in the middle, the anterior and posterior pair being separated only by the anterior paired oculars, which likewise join in the middle. The apical system thus affords a very conspicuous difference from the two other species of the genus. The primary tubercles are more scarce than in PL hir
. Echinoidea of the Swedish South Polar Expedition . The apical system, which is somewhat sunken along the median line, is very interesting, being of a quite primitive structure (PI. XVII Fig. 1). All the four genital plates are distinct, each with a genital pore covered by a long genital pa- pilla; they join in the middle, the anterior and posterior pair being separated only by the anterior paired oculars, which likewise join in the middle. The apical system thus affords a very conspicuous difference from the two other species of the genus. The primary tubercles are more scarce than in PL hirsutus and cinctus. On the abactinal side most of the plates carry only one primary tubercle each, while on the sides and on the actinal side there are 2—3, sometimes 4, primary tubercles on each plate. For the rest the plates are closely covered with miliary tubercles. Only few tubercles occur round the peristome, so that one cannot speak of a bourrelet here. The ambulacral plates along the sternum are likewise covered with secondary
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Keywords: ., bookcentury1900, bookcollectionbiod, bookdecade1910, bookyear1910
