ECHINONEUS CYCLOSTOMUS. 45 
The ambitus in a specimen from Mauritius, Pl. 5, fig. 4, is circular, while 
in two adult specimens, also collected at Mauritius in 1873, only one of which 
is figured, Pl. 5, fig. 3, it is more ovoid in shape with a broad blunt posterior 
end; and the well-defined tubercles, the raised and rounded ambulacra, show 
little similarity to any of the other figures on Pls. 4 and 5. 
Diversity in the shape of the ambitus is also shown on PI. 4, figs. 7, 20, and 
Pl. 5, figs. 7-10; all the specimens figured are from the Pacific and by the same 
collector. On PI. 4, fig. 7, the ambitus is an ellipsoid and the mouth and anus 
are small; the outline of the test is compressed to an ellipsoid with a posterior 
pointed end, and the anal system is elongated, nearly reaching the ambitus, 
(Pl. 4, fig. 20). The same irregularity of the ambitus is shown (PI. 5, figs. 7-10), 
and the actinostome and anal system varies in form and size out of proportion 
to the length of the tests. These specimens were water-worn, the tubercles being 
partly destroyed. 
A specimen from Makemo Island, Paumotu Islands, Exped. ‘‘ Albatross” 
1899-1900, presents an actinostome and anal system toward the right side of the 
test; in other specimens the odd anterior‘ambulacrum also frequently inclines 
toward either the right or the left side. 
The larger of two specimens from Bourbon (Pl. 4, figs. 3, 11), recalls the 
specimen from Lord Howe Island (PI. 5, fig. 2), and the smaller one is identical 
with that from Makemo Island. Three tests from the Gilbert Islands (Pl. 4, 
figs. 12, 15, 18), of nearly the same size, are unlike in shape but are in every way 
similar to the young specimen from Mujeres Island, Yucatan (PI. 4, fig. 19). 
Comparison of two specimens of about the same size from Cuba, one (PI. 4, 
- fig. 23), ellipsoid, and one (Pl. 5, fig. 17), with long ellipsoid ambitus nearly 
one third longer than its breadth, shows little or no conformity to two individuals 
(Pl. 5, figs. 15, 16), from Port Antonio, Jamaica, the larger of which is ovoid 
in outline, the smaller ellipsoid with slightly projecting ambulacra, and large 
actinostome. Of three young specimens also from Port Antonio, the two small- _ 
est (Pl. 5, figs. 12, 13), are ovoid in outline, while the third (PI. 5, fig. 14) is 
ellipsoid with a slight deviation in character towards a young specimen of the 
same size from Mauritius (PI. 5, fig. 5). 
Profile views of the tests strengthen the opinion that variation in shape is 
not wholly due to disparity of age or locality. In two adult specimens of the 
same length, one from Barbados (PI. 2, fig. 3), the other from the Pacific (PI. 3, 
fig. 5), the shape of the profiles are exactly alike, with equally curved actinal 
and abactinal outlines. A third specimen (PI. 4, fig. 9), from Makemo Island 
