126 
REPORT—1847. 
them. Characters of much value, liowevcr, maj'probably be drawn froB 
the internal structure as well as from the external markings of the 
and I quite agree with Prof. Porhes (British Starfishes, p. lio), that t!i« 
characters are of value in distinguishing ajuviejt as well as gentra among tb 
Cidarites’, whilst in the families Clyjira^tvritr. a.iu\ AjE«r/a/i^icmr (in which tk 
spines are almost rudiajentary) their difl’erences are less minute, being ratba 
characteristic of thn entire groups than of their subdirisiona. 
119. I have found the same structure to present itself in the calcarcooi 
plates which form the loss perfect skeletons of the and also ia 
their spines, when these are furnishcil M'ith a calcareous framework, aod ift 
not mere projections of the hard intogumont. Thu spines of tlie lar^ 
master equeatris are jiarlicularly well developed; and both they and the naic- 
miform tubercles on which they aro seated moat distinctly display the nl- 
careous network already ilescribcd. 'I’liey are not united together by a hall* 
and-8ocket articulatioD, the mljacent surfaces of the tubercle and spine beit^ 
flattened, and held together by a membrane. There Is no iDterpositioatif 
solid laniinoj in thn interior of the spine, nor any difference of structure ta 
Its exterior j but the substance is of the same character throughout. Ths 
IS, however, probably the nearest approach exhibited in t\ittAjtmad(sio\\ii 
arrangement of thesti appendages which is ho characteristic in the Jichinida. 
same kind of structure is repeated in tlie family 
■which forms in some respects the transition to the Crinuidal group: buttlif 
calcareous skeleton is hero generally subordinate to the firm and almost 
horny integument. In the Vrhuiideai, on tlie other hand, the cidcureuw 
skeleton is highly developed, ami its structure is extremely cliai-acteristic- 
Miavfi had an opportunity of examining tliis in the ro-cent PenlacriHiis 
M&tus^,^ transverse st-ction of whoso stem is shown in fig. 76 , whilst a [>or- 
tion of the structure more highly magnified is shown iii fig. 77. Froiiun 
inspection ol the latter, the complete oonforniity of its nature, in all esMUthl 
particulars, witlt that of the- calcanHjus testa of the Ecbimis, wdl be at on« 
apparent. 1 here is diaplaycd. however, in the onUrc stem of the PmtOEm^' 
as in the spines of tho Uchimu, a certain ■iiaUct'n, which results from iiolhinj 
e se ^ an t e varying dimenrious of the areoloi in different parts. This pit* 
tern, m the recent species, b formed (as will be seen on inspecting fig.7<>) 
by the presence of five )mir« of rays (strongly reminding us of the medullatr 
ays of an exogenous stem), which extend from the centre towards theu^ 
nnrT *J‘euiaplve8 in the general substance of the stem: 
oRdrm iw iticludcd at their central tcrffli; 
thesr^v diverging rays of each pair. What is the purpose of 
thrioinf. nfTJ’'; apparent; they are, however, constantly present » 
dafrL lu but they do not exist in the lateral arms and appen* 
oKnii.? « or uniform aspect liiroughout. The 
»n fossiIspecimen5,tveDal* 
solidVnrh ; “'’5 as to be converted into 
in *^5. '”*®’ ^^‘'aving into regular rhomboids. The patterns 
c«S fi in distinct species of 
enahlp'jia'f »urvo to aflurrt valuable specific characters, 
.: }, to recognisG the spedes from minute frarrmenL*. Thus in fig- 
altorrpH.;7® set or uroau digitate prolongations, wiucn 
loSr! r "• in which these digitate pro- 
radfatina nS sp^tces included between the 
g plates of ouch i>air are no longer broad and oval, but narrow ainl 
