310 ECHINANTHUS. 



of generic importance. This tendency is, however, not confined to the 

 palaeontologists alone, for recent writers on Echini, and myself among the 

 number, have gone on subdividing genera till each species bids fair, if not 

 to stand in a genus, certainly to occupy the dignified position of a subgenus. 

 A glance at the material here brought together concerning a few species 

 shows how far we have been going in the wrong direction, and I trust that, 

 for certain groups at least, I have been able to show what direction we must 

 give to our examinations of species to have them yield valuable results. 



EC1I1XAXTIIUS. 



Echiuanthus Breyn. 1782. Schedias. (emend.) 



Test thick, more or less elliptical or pentagonal. Ambulacra! petals broad, 

 often swollen, and limited by wide poriferous zones. Five genital pores, ac- 

 tinostome pentagonal, deeply sunken. Anal opening small, infra-marginal. 

 Teeth placed vertically at extremity of jaws, each of which is supported 

 upon two auricles. The interior is tilled by pillars rising from the lower to 

 upper tloors; they are continuations of the double Moors of the ambulacra] 

 and interambulacral chambers, so characteristic of the true Echinanthus, ex- 

 tending from mouth to apex. Johannes Miiller, in his Bau d. Echinodermen, 

 was the first to show the radical difference that existed in the internal 

 structure of the Hat and convex Clvpeaster. 



Miiller has attempted to show that the madreporic body in the regular 

 Echini determined the true position of the axis in the irregular Echini. In 

 the figures he has given of the abactinal system of a number of species of 

 irregular Echini, he has invariably found that it was the right anterior 

 genital plate which was connected with the madreporic body, or the left 

 posterior; and because we have Echinometrae in which the madreporic body 

 is found either on the right or left of the imaginary longitudinal axis, he 

 argues that it must be one of these posterior plates which is invariably the 

 one to give us the position of the axis, and that it is not placing the irregular 

 Echini in a homologous position with the other regular Echini, where the 

 anus gives us the longitudinal diameter without any chance of error, to place 

 the irregular Echini with the madreporic body in the symmetrical rear, with 

 an ambulacrum opposite, as in the regular Echini. The madreporic body 

 in the Scutellidae and Clypeastridae occupies the whole of the mil nil part; 

 it is regular in outline, usually star-shaped, and is not connected in any way 



