MONOGIUPH OF THE ECHINOHERMATA 
OF THE 
CRETACEOUS DEPOSITS IN SOUTH INDIA. 
Sub-kingdom, ACTINOZOA. 
Class, ECHIN ODEUM ATA. 
As one of the three (or perhaps five) principal divisions of the Actinozoa, the 
Echinodermata include the highest organised forms of the Radiate group of the 
animal kingdom ; they are marine animals, free or sessile, or sometimes fixed hy an 
articulated stem, mostly covered with hai’dened integument composed of single 
coriaceous particles, or calcareous plates. The form of the body varies from dis- 
coidal to hemispherical, or globose and cylindrical, with or without appendages which 
indicate the general radiate structure. These arms, or other appendages, have a 
more or less developed prehensile property ; they can generally he re-produced ; and 
the integument is besides often pierced with pores, through which certain pedicells 
or other kind of cDia are protruded, and serve as organs of locomotion. An oral 
opening, surrounded hy a central nerve-organ, a vascular system, &c., are always 
present ; the sexes are mostly distinct, and the young Echinoderm undergoes cer- 
tain stages of metamorphosis, before it becomes fully developed. 
Eew other classes of a well defined larger group of animals show greater 
diversity, both in a purely anatomical as well as morphological point of view, 
than do the Echinodermata. This circumstance, coupled with the comparatively 
great facilities with which their integuments are preserved in a fossil state, made 
the recent as well as the extinct Echinodermata an object of early study, and 
the interest attached to their organisation has occupied the attention of some of 
our best anatomists and morphologists. But it would bo far beyond the scope of the 
present Alemoir to enter into a detailed account of the whole class, because only a 
comparatively very small portion of it finds representatives in the South Indian 
cretaceous dejjosits. 
( 71 ) 
