PHYMOSOMATID/E. 225 



relationship with the Echinometridae but is undoubtedly a Cajnopcdina, though 

 it is so strikingly different from the other members of that group. 

 The ''Albatross" took this species only at the following place: — 

 Station 3991. Off Mokuaeae Islet, Kauai, Hawaiian Islands. Bott. temp. 

 43.7°. 272-296 fathoms. Fne. s., r. 

 Two specimens. 



PHYMOSOMATIDiE' Meissner. 

 General Characteristics. 



Although the superficial appearance of the single living representative of 

 this family, Glyptocidaris crenularis, is quite like that of an Echinus, the structure 

 of the "lantern" shows that it belongs in the suborder Stirodonta Jackson and 

 the ambulacra are also very different from those of the EchinidiB. The ambul- 

 acra are very similar to what is found in a number of fossil Phymosomatidse, but 

 as Duncan (1885, Quart. Journ. Geol. Soc, XLI, p. 449) pointed out, the fact that 

 the pores are not " diplopodous " abactinally prevents our placing the recent 

 species in Phymosoma and necessitates retaining the name Glyptocidaris, under 

 which it was originally described. The structure of the ambulacral plates is 

 very characteristic and is well shown in the Revision of the Echini (PL \T, fig. 2) 

 where it may be seen that the pores are in arcs of five and not in alternate arcs 

 of two and three as one would naturally suppose from the photograph (Rev. 

 Ech., PI. VII ^, fig. 6). Each ambulacral plate is made up of three primarj^ 

 and two secondary elements. The demi-plates lie between the primaries so 

 that the adoral primary element is followed by a demi-plate, then by the middle 

 primary element, then by the second demi-plate and lastly by the aboral primary 

 element. It is easy to see in such a plate a modification of the more simple 

 centrechinid tripartite plate by the introduction of secondary elements in a very 

 different order of succession from what is found in the Echinidae and Echino- 

 metridae. In those families only two primary elements are normally retained 

 in each ambulacral plate, the elements between them being, in most cases, demi- 

 plates. When three primary elements are present, one is adoral and two lie 

 together aborally, while one or more demi-plates follow the adoral element. 



1 In reviving the name Cyphosoma and establishing a family Cyphosomatidoe, for this group, 

 Duncan (1885 and 1889) appears to have overlooked the fact, although the necessary data are given 

 in the Revision of the Echini, pt. 1, p. 151, that Cyphosoma, as a genus of Colcoptcra antedates Cypho- 

 soma, a genus of Echini, by three years. 



