98 HAWAIIAN AND OTHER PACIFIC ECHINI. 



wanting. In the penicillate tube-feet about the peristome and on the subanal 

 plastron, calcareous rods are always developed and there may be other cal- 

 careous particles present but I have failed to find any of any real significance. 

 As a rule, the calcareous particles (aside from the rods referred to) are irregular 

 perforated plates or more commonly curved rods with more or less conspicuous 

 knobs or other projections scattered over them. The various forms have been 

 well figured by Mortensen (1907. Ingolf Ech., pt. 2). 



The Families of Spatangina. 



A satisfactory classification of the Echini here included in the Spatangina 

 is in the present state of our knowledge simply impossible. Mortensen's 

 researches into the growth changes of several species have thrown a great deal 

 of light on some perplexing questions but until we know something of the growth 

 changes in many other genera, particularly some of those with a subanal fas- 

 ciole, we are groping in the dark in the attempt to arrange the genera in natural 

 groups. The simple classification of the Revision in which only two families 

 were recognized does not meet the needs of our present situation, while the 

 classifications of later writers (Duncan, Meissner, Gregory, MacBride) are 

 largely based on characters, concerning the phylogenetic value of which we are 

 still quite in the dark. The classification used by Jackson in the 1913 edition 

 of the Eastman-Zittel Text-book of Paleontology (p. 283-298) represents the 

 best summing up of our knowledge that has yet appeared, including as it does 

 all the Fossil as well as the Recent forms. But I have been unable to use it 

 because it seems to do violence to certain natural relationships, particularly in 

 the division of the Spatangidae into four sections based on the presence or 

 absence of certain fascioles. 



After very long and deliberate consideration of the available fact- - 

 far as the Recent forms are concerned, I have determined not to recognize 

 groups larger than the family in the Spatangina. The classification adopted 

 is purely one of convenience, worked out in the endeavor to make an artificial 

 key to all the genera and species of living spatangoids. A largo part of the 

 data were derived from Mortensen's important publications and the key to 

 the meridosternous families is taken almost bodily from him. But I have 

 examined both test and pedicellariae in nearly all the genera and in a large 

 proportion of the species, so that the various keys are based on first-hand 

 information so far as possible. In recognizing eleven families. I am well aware 



