Revision of the Holothurioidea. 347 
vesicle in the right dorsal inter-radius; one with one additional in 
‘the right ventral inter-radius; and one with one additional in the 
left ventral inter-radius. 
Thus there is an adherence of 93,7°/, to the above described 
modal condition in the number and location of the Polian vesicle. 
The length in centimeters is: mean 7,882 + 0,435; standard devia- 
tion 4,964 + 0,307; coefficient of variability 62,978 + 3,909; range 
0,6—16. 
Stone-canal. — Single, more or less folded and running 
along, or just back of, the free anterior edge of the mid-dorsal 
mesentary (Pl. 13, Fig. 21). Length in millimeters; mean 4,734 + 0,196; 
standard deviation 2,250 + 0,138; coefficient of variability 47,528 
+ 2,926, range 1—10,2. 
The madreporite projects freely (Fig. 21), and is greatly con- 
voluted. Of the 60 madreporites examined, 55 (91,6°/,) are spherical 
in form (Fig. 21), 2 (3,3°),) elongated (Pl. 13, Fig. 22), 1 (1,7%) 
pear-shaped, 1 (1,7°/,) eonical, 1 (1,7°,) irregular, and 1 (1,7°/,) not 
determinable. The spherical madreporite has the following diameter 
in millimeters; mean 1,273 + 0,068; standard deviation 0,750 + 0,048; 
coefficient of variability 58,915 + 3,789, range 0,7—4. 
In the very young (Pl. 13, Fig. 23), the stone-canal is almost 
straight and the folding of the primitive terminal disc into the 
three first lobes is shown. 
SELENKA, 1867, describes the folded madreporite as „composed 
of 12—20 small leaflets“; Crark, 1904, figures a variate with the 
madreporite divided into 6 parts distributed along the stone-canal. 
Calcareous ring. — Not always perfectly preserved, parti- 
cularly in the older specimens. All of the 5 radialia and the 
5 interradialia have anterior prolongations and have the posterior 
margins notched. The radiale is somewhat larger and more deeply 
notched than the interradiale and these differences are accentuated 
with age. In the young (Pl. 13, Fig. 24), the pieces of the cal- 
careous ring have a more definite outline. 
SELENKA, 1867, erroneously deseribes a second, or „upper, cal- 
careous ring“ from which posterior projections extend to the inter- 
radialia of the „chief ring“. SELENKA’S „upper calcareous ring“ con- 
sists of calcareous fibres which bind together the anterior ends of 
all of the pieces of the calcareous ring (LAMPERT, 1885), and the 
posterior projections of SELENKA’S „upper ring“ are merely the anterior 
processes of the interradialia (SEMPER, 1868). TH&EL, 1886, describes 
