376 Agassiz —Paleontological and Embryological Development. 
of the vertical row of pores in the ambulacral area into the ares 
of three or four pairs of Pontes and to the specialization of the 
th the Echinometrade the young thus far observed are 
characterized by the small number of their primary tubercles, 
the large size of the spines, the simple vertical row of pores, 
the closing of the anal ring by a single plate, and the turban- 
shaped outline of the test. Little by little, the test loses with 
increasing age this Cidaris-like character; it reminds us, from 
the increase in the number of its plates, more of Hemicidaris ; 
then, with their still greater increase, of the Pseudodindema- 
tide ; and, finally, of the Echinometrade pro . 
following pari passu, the changes of the test, oe little by little 
their fantastic embryonic, or rather. Cidaris-like appearance, 
and become more solid and shorter, till they finally assume the 
delicately fluted structure characteristic of the Echinometrade. 
The vertical poriferous zone is first changed into a series of 
connected vertical ares, which become disjointed, and form, 
changed to the characteristic heer types. e find, as in 
the Echinometradz, an anal system closed with a single plate, 
and an abactinal system separating in somewhat more advanced 
stages from the coronal plates of the test. This is as yet made 
up of a comparatively small number of plates, carrying but 
few large primary Saherslos, with fantastically shaped spines 
entirely out of pees to the test, but which, little by little, 
with the increase of the number of coronal plates, the addition 
of primary tubercles, and es proportional decrease in ae 
assume more and more the structure of the genus to which the 
young belongs. The original anal plate is gradually lost sight 
of from the increase in number of the plates covering the ana 
system, and it is only among the woven reebit that this anal 
plate remains more or less prominent in the adult. In the 
Salenidz, of which we know as yet nothing of the development, 
this embryonic plate remains Heep a prominent struc- 
— feature of the apical syste 
oung . ha following ing have served as a basis for the preceding 
laaivnts of the roth oe or ors the Desmosticha: Cidaris, Dorocidaris, 
idaris, Aiba Podocidaris, Strongylocentrotus, Echinometra, ae 
Toxopneustes, Biippouiol, muniniopletras, Temnechinus, and Trigonoci 
