02 ECHINOIDEA. I. 



Lambert (238. a). 



Fam. E c h i 11 o m e t r i d æ. 

 Subfani. Echininæ. 



Tribus. Oligoporinæ. Triplechinæ^ ScJiizechinæ. 



— PoU-porinæ. Sphærechinæ. Hcliocidariiiæ, Acrocladinæ. 



The characters, on which the systems hitherto established have chiefly been based, are: the 

 niimber of the pores, the breadth of the ambulacral areas, the slits and form of the test. Desor^) is 

 the first aiithor, who iises the number of the pores as a priuciple of division, dividing the forms 

 belonging here into «01igopori» and «Polypori». In this he is followed by all the later authors (even 

 if they do not nse the expressions of «01igopori^ and «Polypori») with the exception of Pomel and 

 Bell. In the essay on the Echinometrids quoted above, Bell has given a thorough criticism of this 

 feature, and has shown that it is by no means a natural principle of division, in spite of the assertion 

 of Agassiz (Rev. of Ech. p. 423) that ..this division, although it appears a numerical one, is yet one 

 of great physiological importance, as the mode of growth of the poriferons zone in these two families 

 is totally inilike-'. I must assert, still more strongly than has been done by Bell, that this division 

 is a quite numerical one, not at all corresponding to the natural relation of the forms. Moreover it 

 cannot be carried through at all, some species having on the lower ambulacral piates (i. e. as young 

 individuals) trigeminate pores, on the others multigeminate ones. Besides the instances mentioned by 

 Bell: Ec/nnostrep/it(s, Strongylocentr. drubachicnsis^ Echiiiomctra iiiacrostoma and other Echinometra- 

 species, I can name 'i,Strongylocentrotust> albus and lividus that have also only three pairs of pores in 

 the lower ambulacral piates. Also in young Sphærechinus granulan's trigeminate pores may be found 

 in the lower piates, and this feature, I think, may be taken to be found iu all polypore forms. When 

 Bell, in his group of Echininæ^ uses the number of the pores as a base of further subdivision, I can- 

 not agree with him; so mucli importance is not due to this feature, it can by no means be regarded 

 as more than a generic character, and I should not wonder, if in some cases it should prove to be no 

 more than a specific character. At all events the number of the pores has only slight importance 

 or none at all with regard to the natural grouping of the genera; Pomel seems to be the only author, 

 who has hitherto seen this faet. 



The breadth of the ambulacral areas is used by Gray as a distinguishing character. That it 

 is especially unfortunate is shown by the result, as Gray thereby is brought to the uniting oiAvibly- 

 pneustes^ Holopneustes, Boletia^ and Hippoiioc into one family, wliat is absolutely wrong; neither has 

 any author followed him in this respect. 



The slits of the test are used by Pomel and Troschel, by the latter, however, only as a sub- 

 ordinate character, the number of the pores being used as the first principle of division, so that only 

 the forms with trigeminate pores are referred to his family Tripneustidæ^ while Spliærechinus and 

 Pseudoholetia are referred to the family Toxopneustidæ. — Agassiz says of the deep slits of the test 

 in Sphærechinus (Rev. of Ech. p. 451): <the presence of deep, sharp cuts in the actinal system ... are 

 simply quantitative characters, the valne of which a better acquaintance with the subject will deter- 



I) Synopsis des Echinides fossiles. 1855. 



