MEM, M. C. Z., IX. No. 2.—ECHINODERMATA. 35 
12-18. Echinus lividus. From Johannes Miiller, Vierte Abhandlung (1850-51), Pl. VI., VIL. Quoted above. 
12. 
13, 
17. 
18. 
19. 
20. 
28. 
29. 
29. 
30. 
A. First pair of dorsal arms. b. Stomach. 
B. Second pair of dorsal arms. v!. Intestine. 
rE. Second pair of oral arms. c. Anus. 
F. First pair of oral arms. d. Cord of vibratile cilia. 
a. Mouth. f. Vibratile epaulettes. 
a, Csophagus. 
Pluteus on the sixteenth day after artificial fecundation ; this Pluteus was remarkably slow in its development. 
14. Pluteus on the eleventh day after artificial fecundation, but more advanced than the preceding stage. 
13, seen obliquely from the side ; x is the outline of the depression in which the mouth is placed. 14, seen 
from the mouth side. 
. Somewhat more advanced Pluteus, on the seventeenth day, seen obliquely from the dorsal side, shows the rel- 
ative position of the calcareous rods, of the arms, and of the cord of vibratile cilia. 
. Somewhat older Pluteus, in which the arms have greatly lengthened, and there is a slight swelling of the 
vibratile cord at the base of the dorsal arms, denoting the position of the future vibratile epaulettes. 
Fully developed Pluteus, with vibratile epaulettes ; the young Echinus is well advanced. 
Stage in which the young Echinus has resorbed the greater part of the Pluteus ; only a small part of the oral 
extremity and short pieces of the rods of the arms of the larva are left. The rudimentary embryonic spines, 
x, are quite prominent ; the ambulacral suckers, y, are clearly seen; one of the longer tentacles projects 
beyond the disk, and a few pedunculated pedicellarie have made their appearance. 
19-27. Echinocyamus pusillus ? 
19-21. From Johannes Miiller, Vierte Abhandlung (1850-51), Pl. VIII. Quoted above. 
A. First pair of dorsal arms. a, (Esophagus. 
F, First pair of oral arms. b. Stomach. 
a. Mouth. bo’. Intestine. 
Young Pluteus, seen from the ventral side. 
The same, seen obliquely in profile from the dorsal side. 
. Somewhat older Pluteus, in which the second pair of oral arms is already formed. It is somewhat problemat- 
ical if the stages of figs. 19-21 are the younger stages of figs. 22-24. 
22-27. From Johannes Miiller, Siebeute Abhandlung, 1855, Pl. VIII. Quoted above. 
a. Mouth. d. Intestine. 
b. (Esophagus. e. Anus. 
c. Stomach. 
. Young Piuteus, with two dorsal and two oral arms, seen obliquely, looking into the mouth cavity. 
. Somewhat older Pluteus, seen from the dorsal side ; the second pair of oral arms has made its appearance. 
. Fully grown Pluteus ; the young Urchin is not yet far advanced. 
. Pluteus in which the resorption of the anal extremity is well advanced, the young Urchin occupying the whole 
of the anal extremity of the Pluteus ; the oral extremity is still nearly unchanged. 
5. The young Urchin seen in profile, after the complete resorption and disappearance of the plutean appendages. 
7// in diameter. The odd tentacles have already well-developed suckers. 
. The same young Urchin as fig. 26, under compression, showing the five teeth, the limestone plates of the 
actinostome, and the single row of embryonie spines placed round the ambitus. 
28. Echinarachnius parma? From Alexander Agassiz, Revision of the Echini, 1874, Part IV., p. 727, fig. 65. 
Illust. Cat. Mus. Comp. Zodl., No. VII. Part IV., 1874. 
Well-advanced Pluteus, remarkable, like the problematic Zchinocyamus Pluteus, fig. 24, for its rounded anal 
extremity : a, mouth ; a’, esophagus ; d, digestive cavity ; 7, intestine ; am, anus. Seen from the mouth 
side. 
Echinus acutus? From Johannes Miiller, Ueber die Larven und die Metamorphose ... . (1846), Pl. V. 
Quoted above. 
Fully developed Pluteus, with rounded anal extremity, large vibratile epaulettes, and comparatively short arms. 
Seen from the mouth side. A, first pair of dorsal arms ; B, second pair of dorsal arms ; a, mouth ; a’, cesoph- 
agus ; 5, digestive cavity ; d, cord of vibratile cilia ; ¢, caleareous rods of arms ; f, vibratile epaulettes. 
30. Echinus brevispinosus. From Johannes Miiller, Siebente Abhandlung, 1855, Pl. I. Quoted above. 
Fully developed Pluteus, seen from the dorsal side. This Pluteus is remarkable for the short pair of anal 
arms developed at the posterior extremity. 
