III. Asteroidea. 1 3 



morphological importance, He does not agree with Perrier in regarding the 

 pedicellariae as furnishing characters of the highest taxonomic value. They 

 do not appear before the spines in the embryo, but are modified spines, as sug- 

 gested by Agassiz, and the more complex forms of them are the most recent, not 

 the oldest. Neither is the shape of the odontophore or basal interbrachial 

 plate a character of such high systematic importance as supposed by Viguier. 

 There is often more difference between the odontophores of congeneric species 

 than between those of distinctly separate genera. In some families (Porcellan- 

 asteridae, Brisingidae y this plate is exposed on the actinal surface, between the 

 aboral ends of the two mouth plates. - - Among the fundamental morphological 

 characters which are common to the whole class there are three which are cor- 

 related in such a way as to warrant their being ranked as ordinal factors in a 

 natural classification. In one group of the Starfishes (Stenopneusia) the papulae 

 or gills are confined to the abactinal surface, while in another (Adetopneusia) they 

 may also occur on the lateral walls or on the actinal surface. This latter group is 

 the higher or more complex, and its members pass through a Stenopneusian stage in 

 their early development. --The ambulacral skeleton and the correlated series 

 of tube-feet exhibit two modes of growth. In the Leptostroteria the production of 

 parts is accelerated in relation to the growth of the Starfish, so as to crowd the plates 

 together and produce a quadriserial arrangement of the tube-feet. In the actinosto- 

 inial ring the ambulacral elements become the most prominent and define the moutli- 

 characters, the adambulacrals being retarded and relatively insignificant. But in the 

 Eurystroteria the production of plates is retarded or follows the general develop- 

 ment' of the skeleton, and the tube-feet remain biserial, while the adambulacral 

 plates are the most prominent in the actiuostomial ring. This is the more primi- 

 tive condition, but is only a transitory one in the development of the Leptostro- 

 teria. - The ambital skeleton, formed by the marginal plates and their 

 supplementaries, when present, furnishes important systematic characters. In the 

 Phanerozonia the marginals develope rapidly, becoming prominent and conspi- 

 cuous in the adult ; while in the Cryptozonia their relative size as regards the 

 body is conspicuously diminished in the adult as compared with the younger stages 

 of growth, which are markedly Phanerozonate. Hence the Phanerozonia are older 

 than the Cryptozonate group, and the latter indicates a divergence in character and 

 a modification in form which are correlated with the development of other organic 

 systems.- - Thus then three of the most important class-characters of the Euaste- 

 roidea exhibit two modes of presentment, and by means of any one of the three 

 the class may be divided into two groups, one of which is apparently older than 

 the other. The divisions thus made are essentially equivalent in each of the three 

 categories, and they thus define two strictly natural orders, the name-characters 

 of which are best furnished by the marginal plates, both on account of their im- 

 portance in the Asterid skeleton, and because their peculiarities and relations are 

 easily observed. 



Phauerozouia = Stenopneusia = Eurystroteria. 



Cryptozonia = Adetopneusia = Leptostroteria. 



The marginal plates in the interbrachial arcs of the Porcellanasteridae bear from 

 1-12 peculiar cribriform organs, each consisting of numerous compressed 

 lamellae arranged in vertical parallel lines. These are composed of smaller la- 

 mellae, each built up of several series of united rods, and the whole organ is 

 ciliated. In one young individual the madreporite, which is on the extreme margin 

 of the disk, is embraced by the cribriform organ. The latter probably acts as a 

 percolator and corresponds to the fringes of the delicate miliary spinelets in Astro- 

 pecten and to the fascicles of irregular Echinids. -- The adambulacrals and mouth- 



