. Echinoidea of the Swedish South Polar Expedition. Sea urchins. 62 TH. MORTENSEN, (Schwed. Siidpolar-Exp. the periproctalregion of PL hirsutus (Fig. 14), which has not been given in the slngolB Echinoidea, where this species was described.) The periproct is not sunken; the whole posterior end sloping rather gently. — Regarding the other interambulacra it is only to be noticed that the anterior paired ones agree with those of the other species in the second plate being compound (2 + 2). — The anterior ambulacrum is distinctly depressed towards the mouth; towards the apical system the plates be
. Echinoidea of the Swedish South Polar Expedition. Sea urchins. 62 TH. MORTENSEN, (Schwed. Siidpolar-Exp. the periproctalregion of PL hirsutus (Fig. 14), which has not been given in the slngolB Echinoidea, where this species was described.) The periproct is not sunken; the whole posterior end sloping rather gently. — Regarding the other interambulacra it is only to be noticed that the anterior paired ones agree with those of the other species in the second plate being compound (2 + 2). — The anterior ambulacrum is distinctly depressed towards the mouth; towards the apical system the plates become somewhat lower than in the other ambulacra. In the posterior paired ambulacra it is the 4th plate which reaches within the fasciole, in the usual 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. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Mortensen, Th. (Theodor), 1868
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Keywords: ., bookcentury1900, bookcollectionbiod, bookdecade1910, bookyear1910
