OF SOFTIIERX INDIA. 
3 
circumference, or sometimes n ith perforations near, or incisions at, the margin. The 
test is composed of five pairs of ainbulacral, and alternating uitli the former five 
iuter-amhulacral zones of plates, making a total of twenty meridional scries ; only 
in some of the palmozoie forms, the so-called Tcsselati, this number of series rises 
to 35, and even to 75. The plates are joined to each other by plain sutures, firmly 
connected by organic substance, forming a solid test. In very few cases, as, for 
instance, in IleUmUes, is the nuiaher of amhulacral series larger than ten. 
The pediccllar pores in the ambulacra are either scattered, or generally they 
arc situated near the outer basal margin of each plate, cither in continuous or sim- 
ple series, extending from the apex tn the aperture (Gklaris, Ecliinus) ; sometimes 
they become slightly less distinct Avith the distance from the apex, but tlie scries 
are still continuous, or very nearly so (Dysasler, Echinoncm) ; or the series of 
pores are partially interrupted, the two pores in each ambulacrum being well dis- 
tinguishable on the upper side of the test, terminating ahru]itly before or when 
they reach the periphery, after which sometimes a few single pores are traceable, 
occasionally re-appearing again near the peristome of the aperture as a so-called 
rosette; the upper portion of this kind of poriferous series is called suh-petaloid 
(many Eemiaster , Eupatayus, etc.) Lastly, there are instances in which the pori- 
ferous zones become entirely interrupted, forming on the upper side round the apex 
five elongated, ovate, almost perfectly closed regions ; this form is called petaloid, 
and is best marked in Clypeaster and its allies. As regards the pores themselves, 
composing the pair in each series, they arc cither equal and close together, or far 
apart, uni- or hi- or poly- gcminal ; the outer pores are sometimes larger and 
elongated, and again they are occasionally connected by a groove with each 
other, in Avhich case they arc said to he yoked. In the case of the petaloid or 
suh-petaloid form of the poriferous zones, these arc situated in furrows or not. All 
these characters arc of the utmost importance in classification. The form of the 
poriferous zones is mostly a family or sub-divisional character ; tlic form and relative 
position of the pores is most useful in distinguishing genera, Avhile the relative 
number of pairs of pores is generally very constant in different specimens- belonging 
to the same species. 
The surface of the test is ornamented Avith tubercles and spines, both of Avhich 
arc extremely variable. The tubercles Avhen of large size arc called primary ; they 
arc composed of the mamelon, which is the convex top part of the AA'hole ; the boss, 
or conical prominence, AA'ith a smooth or crcnulated upper edge, and the areola, or 
excavated space, surrounding the boss. Smaller tubercles are called secondary, or 
minute, or Avhen they arc very small, they are designated granules, sometimes Avith 
similar gradations, as in the case of the tubercles. The tubercles arc in the centre 
of the mamelon perforated or not. To the mamelon the spines, or radiolcs, are arti- 
culated, Avhich vary from an almost globular to a cylindrical, club-shaped, or acieu- 
late form. Both the radiolcs and tubercles arc, like the remainder of the test, 
covered Avith an epidermis ; their shape and relative size arc important in specific 
( 73 ) 
B 
