170 HAWAIIAN AND OTHER PACIFIC ECHINI. 



only by the " Challenger." Its relationship to the other Echinothuridoe is 

 still unsettled and more material is greatly to be desired. There is an 

 interesting parallelism between this genns and Micropyga in the struct- 

 ure of the stalks of the pedicellariae ; each is the only genus in its family 

 with these stalks noticeably different in structure from those found in 

 the allied genera. 



There appear to be two quite distinct species of Kamptosoma which 

 may be separated from each other as follows : 



Abactinal ambulacral areas not noticeably expanded just above ambitus, 

 composed of high plates not wider than those of the actinal side, 

 their width not exceeding twice their height and sometimes not 

 equalling it asterias. 



Abactinal ambulacral areas markedly expanded just above ambitus, 

 composed of low plates, much wider than those of the actinal 

 side, their width often four times the height indistinctum. 



Kamptosoma asterias Mortens. 



Phormosoma asterias A. Agassiz, 1881. "Challenger" Ech., p. 104 ; PI. XID, figs. 7-9. 

 Kamptosoma asterias Mortensen, 1903. " Ingolf " Ech., p. 60. 



Off the coast of Chili; 2160 fathoms; "Challenger" Station 299. 



The type-specimen of this interesting species, 30 mm. in diameter and 

 doubtless young, is still unique. 



Kamptosoma indistinctum A. Ag. 



Kamptosoma indistinctum A. Agassiz, 1904. Panam. Deep-Sea Ech., Mem. M. C. Z., 

 XXXI, p. 110 ; PI. 50. North of the Society Islands, East of Maiden Island, 

 2600 fathoms; "Challenger" Station 272. 



In spite of Mortensen's decision to the contrary, we think this species 

 must be maintained, unless the differences of ambulacral structure referred 

 to above, which distinguish this species from the preceding, can be shown 

 to be unreliable. We beg to call attention to two facts which bear on 

 this point. First : it was only in this species that Mortensen found the 

 large, characteristic tridentate pedicellariae ; they were not found in the 

 type of asterias. Second : Mortensen says that secondary ambulacral plate 

 elements are wanting, except " nearest to the peristome a single one may 

 be found." Unfortunately he does not say whether this was observed in 

 the type of asterias or in a specimen from " Challenger" Station 272. If in 

 the former, it gives us an additional specific character; if in the latter, 

 we are at a loss to reconcile his statement with the real condition in in- 

 distinctum (see Panam. Deep-Sea Ech., p. Ill, fig. 151 and Plate 50, fig. 3). 



