98 



ECHINOIDEA. II. 



the veitex being at the end of the posterior petals. The sides of the test are almost vertical, the 

 actinal side almost flat. The periproct is sitiiated near the abactinal side, in a slight furrow. The 

 ambulacra ave very little deepened. — The j'oung specimens are somewhat more egg-shaped, bnt the 

 posterior end is high as in the larger specimens, the ontline in profil being niainly the same; only 

 in the specimen of 3""" length the posterior end is yet rather sloping, the anal opening being very 

 near the apical system. 



To give a detailed description of the strnctnre of the test would be superflnons after the 

 elaborate analysis and fignres given by Loven, only a few additional remarks can be given on 

 acconnt of the larger material at disposal. — In the yonnger specimens the peristome and month is 

 as yet qnite embryonal, the labrnm not prominent at all; in the specimen of 3"'™ the peristome is 



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. V.46); 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 sizes. 



