152 HAWAIIAN AND OTHER PACIFIC ECHINI. 



plates is generally only to be seen in dried specimens. But the Echinothu- 

 rids are only very little adapted for preservation in dried state, and if the 

 material in hand be slight, one does not like to destroy it for the sake of 

 determination." — "The sphaeridiaB . . . show no differences so great that 

 they can be of any systematic importance. The pedicellarite, on the other 

 hand, are of the greatest importance with regard to the classification." It 

 is because we do not think that the " spines, the pedicellarige, the tube-feet, 

 and the spicules " should " bear the principal part " in a satisfactory class- 

 ification of the Echinothurids, and because we consider " the structure of the 

 test," using that phrase in the widest sense, to be of " all predominant 

 importance" that we are obliged to dissent from Mortensen's classification. 

 Moreover, we find the Echinothurids admirably adapted "for preservation 

 in dried state " ; all of the photographic plates given herewith and those 

 in the report on the Panamic deep-sea Echini (Mem. M. C. Z., XXXI) are 

 from dried specimens ; so far from drying, destroying the specimens, it pre- 

 pares them very satisfactorily for systematic study. As will be noted in our 

 discussion of the genus Phormosoma, we find the sphteridia afford an in- 

 teresting character of real " systematic importance." 



Our studies of the Echinothuridse have led us to the conclusion that 

 there are six natural genera in the family. We believe Mortensen is right 

 in limiting Phormosoma to the group of species allied to placenta, but we 

 fail to find any character of importance by which his genera Hygrosoma 

 and Tromikosoma are to be distinguished from Echinosoma Pomel. Of 

 course, if one considers the possession of certain peculiar pedicellariae, in 

 small numbers, by some individuals, as a valid generic character, then one 

 must accept Mortensen's groups, but, as we have often stated, we cannot 

 believe such a criterion is right. The peculiar ambulacra of Kamptosoma 

 and Sperosoma warrant the recognition of those genera, while the numer- 

 ous, small, uniform primary tubercles, bearing sheathed spines, which 

 cover the abactinal surface of Asthenosoma, make that genus, as limited 

 by Mortensen, an easily recognized group. We have not been able to 

 find any satisfactory characters by which Mortensen's genera Hapalosoma 

 and " Calveria " are to be distinguished from Arseosoma, and we have 

 therefore united the three groups under the last name. 



The six genera which are thus accepted by us may be distinguished 

 from each other as follows : 



