+t TROPICAL PACIFIC ECHINI. 
“Tn size, Echinonéus rarely exceeds an inch in length. The specimens 
taken range from 4 to 27 mm. Most of them are between 8 and 18. The form 
of the test is very variable, the proportions of width to length, height to width, 
ete. showing much diversity. (In 1897, a bare test was found 42 mm. long.) 
“Tt is quite possible that large specimens occur in deeper water, outside the 
reef, but this is simply a conjecture. 
“The absence of specimens less than 4 mm. long is greatly to be regretted, 
but it seems almost certain that such young ones must occupy a different habi- 
tat from the adults. Since it is probable that there is a free swimming larval 
stage, it is quite possible that the absence of specimens under 3 mm. in length 
from the sand where the adults occur may be explained as follows:— after the 
metamorphosis, or at least at the conclusion of the free-swimming stage, the 
young Echinonéus settles on the calcareous Algae, eel-grass, or other vegetation 
surrounding undisturbed fragments of coral rock on the sand-flat, and only 
slowly moves downward to and into the sand beneath the rock. By the time 
the sand is reached, the Echinonéus is 2 or 3 mm. in length.” 
Echinoneus cyclostomus Leske. 
THE OUTLINE OF THE AMBITUS. 
Plates 4, 5. 
With material limited to a few specimens the specific characters seem easily 
distinguished, but with an abundance of specimens the supposed differences are 
at least doubtful. Pls. 4 and 5, give a far better idea of the characteristics 
of the test than any description. 
The figure of a fossil E. michaleti given by Cotteau and of de Loriol’s E. 
abnormalis from Mauritius, are exactly identical in outline with the one shown 
(Pl. 5, fig. 4) from Mauritius, and also with that collected in 1868 by Count 
Pourtalés at Caryfort Reef, Florida (PI. 5, fig. 17) all of which have an almost 
circular ambitus; the anal system in the smallest Florida specimen being much 
longer than in the other. 
In comparing two specimens of nearly equal length from the same locality, 
Lord Lowe Island, N.S. Wales (PI. 5, figs. 1, 2), it will be seen that the ambitus 
of the smallest, fig. 1, is between an ovoid and a pentagon in shape, and that the 
anal system is elongated, while in the other, fig. 2, the ambitus is unevenly 
pointed at the anterior end with a longer distance between the anterior ambula- 
crum on the left side and the anal system is short. 
