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OF THE REGULAR ECHINOIDEA. 369 
more or less branched, running from side to side of the spiculum ; they open on the sur- 
face in the depressions between the spines; the smaller hooked spicula are occasionally 
found at the base of the ambulacral tubes. In a fragment of membrane obtained from 
the interior of the shell, delicate branched spicula were found in moderate abundance. 
The spicula of an Echinus (Tripneustes*) from the New Hebrides, and called by the 
natives Néhvei, are also extremely interesting, as they approximate in character the 
miliary and tentacular spicula of Synapta and Chirodota, in which the dumb bells, passing 
into the hooked condition, are of such frequent occurrence: their various forms are 
shown in Plate L. fig. 5, a; and in Plate L. figs. 10, 11, the spicules of Chirodota 
and Synapta are figured for comparison. 
Although in Acrocladia the test and spines attain so great a size, the spicula are very 
scanty in comparison with most other genera. Those of the ambulacral tubes are about 
as numerous as in Echinus; they are, however, more long and straight, with abruptly 
curved points (Plate L. fig. 6, a). I have not been able to find any in the ovaries or 
intestine; but the ambulacral vessel contains some similar to those of the internal parts 
of Echinus. 
In Podophora I have found spicula only in the ambulacral tubes, not differing from 
those of Echinus, although I had abundance of the internal parts for examination, show- 
ing in this respecta greater affinity to Acrocladia than Echinometra, in which genus 
it used to be included. (Plate L. fig. 7.) 
In Mespilia spicula were found in the ambulacral tubes and ovaries ; they were of the 
bihamate form, large, but slender. (Plate L. fig. 8.) 
Bihamate spicula were also found in a fragment obtained from the exterior of the 
shell of a Temnopleurus : they were mixed with irregular perforated plates ; so it may pro- 
bably be considered a portion of the external branchiæ, in which such plates are, I 
believe, of constant occurrence in most, if not all, of the genera in which these organs 
are present. (Plate L. fig. 9.) 
I was unable to find any in Arbacia, although the ambulacral tubes, intestine, and 
ovaries were examined with great care. 
I have only, in concluding, to return my most sincere thanks to Dr. Gray and Mr. 
Flower for the kindness with which they permitted me to examine the valuable speci- 
mens in their charge ; nor can I fail to record my obligations to the late Mr. S. P. Wood- 
ward, who most freely allowed me to study those of his private collection. 
belongs to the genus 
* Since the above paper was read, I find that the Echinus from the New Hebrides really 
The propriety of this, 
Tripneustes, E, Drübachiensis is also placed with E. lividus, &c., in that of Toxopneustes. s 
together with some other subdivisions of the old genera Echinus and Cidaris, seems to me, however, to be doubtful. 
