. Echinoidea. Sea urchins. Fig. 16. Peristome and adjoining part of the test of a young Hetniaster expergifiis, y^m in length. 25/,. Fig. 17. Apical system of a young Hemiasier expergitus, j""" in length. 25/1. The outline of the smaller ambulacral piates and of some of the inner iuterainbulacral piates not quite sure. qnite pentagonal; the peristomial mcmbrane is fnll of small somewhat concentrically arranged piates (Fig. 16). In the larger specimens the labrnm becomes by and by rather prominent, a little poiuted, with the edge a little thickened and reverted. Its jjosterior ed
. Echinoidea. Sea urchins. Fig. 16. Peristome and adjoining part of the test of a young Hetniaster expergifiis, y^m in length. 25/,. Fig. 17. Apical system of a young Hemiasier expergitus, j""" in length. 25/1. The outline of the smaller ambulacral piates and of some of the inner iuterainbulacral piates not quite sure. qnite pentagonal; the peristomial mcmbrane is fnll of small somewhat concentrically arranged piates (Fig. 16). In the larger specimens the labrnm becomes by and by rather prominent, a little poiuted, with the edge a little thickened and reverted. Its jjosterior edge reaches, in the smaller sjDccimens, only to the middie of the adjoining ambulacral piates I. a. i and V. b. i (Comp. Loven. PI. ); in somewhat larger specimens it reaches to tlie end of the first ambnlacral piates, or a little farther on the right side, as in Lovén's Figure 114 (and his PI. V. 47), and in the grown specimens it reaches to the middle or even to the end of the second adjoining ambulacral plate on each side (PI. II. Fig. 4); generall\- the ambulacral piates of V. b. are a little shorter than those of I. a, so that the right side of the labrum ajDpears to reach a little farther than the left, but it is really symmetric. In the larger specimens the inner ambulacral piates are comparatively much smaller than in the young specimens, and their outline likewise is different. But though it thus looks rather different in the young and grown specimens, no character for eventnally distinguishiug two species is to be found hereiu; it is a difference due only to age, all transitional stages being found in the corresponding intermediate 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), 1868-1952. Copenhagen, Printed by Bianco Luno
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Keywords: ., bookcentury1900, bookcollectionbiod, bookdecade1900, bookyear1903
