PROCEEDINGS OF GEOLOGICAL SOCIETIES. 
489 
The author commcncod by imlicatiug the position of the EcliinidiE as a hirgc 
and important seetion of the Radiatii, iiud pointed out the several steps in the 
seri(!s whieli connected t lie completely cii'cular types with those having a marked 
tendency towards bilatcrality. 
The principal cliaracteristics of the order were then ennmcratcd, commenc- 
iiip; witli a dcscrijition of the calcareous shell, or test, constituting an internal 
and integral portion of the animal being secreted l)y and enclosed within 
organized membranes, and j)articipating in the life of the organism — the homo- 
logiu! of the vertebrate skeleton rather than of the shell of the moUusca. 
Tlie several elements of the tests were then described, the ten columns of 
small ])lates constituting the ambidacra, the ten larger, the intcrambulaera, 
separated from each other by ten rows of holes — the poriferous zones. The 
tnoercles with which these plates are studded were then enumerated — the large 
primaries, the secondaries, the minute granides, and the mili;u-y granulation. 
T'he varities of form and arrangt-ment of the pores were next reviewed, and 
then the relative position and varying shapes of the two great orifices, the 
receptive and rejective poles. The internal organization was briefly glanced at, 
and the principal viscera enumerated. The apical disc was described, its 
separate elements, the ovarian, and ocular plates, their relative natm-e and posi- 
tion indicated. 
The varieties of spines, their forms, sculptui'e, attachment, and the structure 
of their parts, was also pointed out. 
The author next proceeded to dwell upon the relative value of the external 
organs in classification, begimiing with the position of the mouth and vent, and 
especially urgmg attention to the i)hysiologieal import of these and the other 
organs, and even of scidptural decoration of the test as indicative of purpose 
and design, and not to oe considered merely valuable as means of classifica- 
tiou. He dwelt upon the necessity of taking into consideration the mutual 
relations of the great vital functions of digestion, reproduction, vision, and 
locomotion as the basis of any sound natural arrangement. The position of 
the vent either within or external to the elements comprising the apical disc 
was shown to be a good character by which to divide the order into two great 
divisions — the ExoeycHe and the Endocyclie Echinidas ; the structure of the 
ambidacra and poriferous zones, taken in connection with the position of the 
vent, formed good secondary characters for groujiing the genera into natiu'ai 
families, while the former were well defined by the form, number, and arrange- 
ment of the spines and tubercles, the miliary granidation, the size and number 
of elements of the apical disc, and the position of the vent taken coUectively. 
The author then intimated that tlie limits he had assigned to hhnself did not 
permit of any indication of sj)ccific characteristics, but tliat he should content 
himself witli an enumeration of the principal pomts of the generic classification 
of 1 he EchinidiE of the chalk, and of the families to wliich they belonged. 
He then proceeded to describe by the aid of numerous large diagrams the 
generic distmctions of Cidaris, Diadema, Cyphosoma, Echinus, Salenia, Dis- 
coidea, Galerites, Cacatomus, Nucleolites, Catapygus, Pyi'ina, Hoiaster, 
Cardiaster, Ananchytes, Micraster, Hemipneustes, Heniiaster. 
A vote of thanks having been passed, the author stated that in selecting this 
subject he had been guided by an old admiration of an order which, from 
Hvmg in a chalk-district, had attracted his attention in early youth, and he 
had often felt the want of such a guide as the observations he had just made 
would furnish. He particidarly denied aU claim to originality, his only merit 
bemg that of having collected into one view, materials which lay scattered in 
a number of rare and costly works. 
