2 
CRETACEOUS ECIIIXODERMATA 
The whole class is somewhat differently sub-divided by various authors. The 
most usually adopted classification is that into Uolutiiumioidea, Ecbixoidea, 
Asteeowea, Crieowea, and Blastoibea. Detailed descriptions of the different orders 
will bo found in Dujardin and Ilupes’ Nouv. Suite a Buffon, Bronn’s Klassen 
and Ordnungen des Thierreiclies, and other general zoological works. Dr. Wrightj 
who promises to gh’c a comprehensive account of the class at the conclusion of his 
work* on the British cretaceous Ecliinodermata, adds to the five orders, above 
referred to, the S ivueiguloibea, and separates the Obuiueoibea from the Asteeojbea, 
and the Cystoibea from the Crixoibea. 
Three orders of the Ecliinodermata are represented in South India. The 
Crixoibea by two or three species, the Asteroibea by a single one, and the 
Eceixoidea by thhty-eight. As the last includes the most highly organised types, 
I will, according to the general arrangement adopted in these monographs, begin the 
description with the Ecuixoibea; and as this is at the same time the only order of 
Avhich a considerable variety of species has to be noticed, and as more extensive 
discoveries of Echinoids in the South Indian cretaceous deposits are certainly to be 
expected, I will preface the detailed descriptions by a brief anatomical account, 
giving also an abstract of the general classification. 
I. Order. ECHINOIDEA. 
General Character. — Echinoderms icith an oml, or round, or polygonal, more 
or less spheroidal or depressed, free body, surrounded hy ticenty or more ranges of 
polygonal calcareous plates, closely fitting against each other ; ten of these ranges, 
called the ambulacra, are always provided with continuous or interrupted scries of 
pores for the passage of retractile pedicells, ichile the outer surface of all is covered 
with more or less distinct granules or tubercles to ichich calcareous spines of various 
shapes are articulated ; mouth inferior, central or cxcentric, internally sometimes 
provided icith a complicated, masticatory apparatus ; anus very variable in position, 
above central or excentric, or marginal, or below excentric ; three to five genital 
and five ocular plates always form the a2)ex, the madreporiform plate is united with 
the right anterior genital ; the sexes are distinct. 
Tliis general character referring to the test requires some explanation, in order 
to show which points should particularly be consulted in the determination of 
species and genera ; and as the internal organisation is intimately connected with 
that of the solid test, this being very variable in structure and form, it might be 
useful here briefly to allude to the principal anatomical points ; this Avill also indicate 
the importance Avhich can be attached to the diflerent parts of the test to be 
described immediately. 
As regards the form of the test, it may be remarked that in by fixr the major- 
ity of cases it is spherical or hemispheroid, round, or more or less ovate, in 
* Published by the Pala’outograpliical Societ}’ of Loudon. 
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