156 HAWAIIAN AND OTHER PACIFIC ECHINI. 



of any other species, but further material is necessary to determine how 

 constant these characters are and what are the limits of their variation. 



Phormosoma verticillatum Mortens. 



Phormosoma verticillatum Mortensen, 1904. Ann. Mag. Nat. Hist. (7) XIV, p. 90; 

 Pis. IV, figs. 1, 2 ; V, figs. 15-17. 



Bay of Bengal ; 678 fathoms. 



In addition to the characteristic verticillated abactinal spines, Mortensen 



points out the small actinal and abactinal systems as features in which this 



species differs from placenta ; thus the abactinal system of a, placenta, 66 mm. 



h. d., is about 30 % h. d., while in verticillatum, 63 mm. h. d., it is only about 



20. The color of verticillatum may prove to be a good character, for although 



the specimens are bleached, there is some indication of violet actinally, not a 



common color in the genus. 



Phormosoma rigidum A. Ag. 



Phormosoma rigidum A. Agassiz, 1881. " Challenger " Ech., p. 104 ; PI. XHa, figs. 1-4- 



Off New Zealand ; 700 fathoms. 



Although the specimens on which this species is based are small, the 

 largest only 40 mm. h. d., the abactinal ambulacral pores are quite charac- 

 teristic, and we do not think they can wisely be referred to either placenta 

 or bursarium 



Phormosoma adenicum Dod. 



Phormosoma adenicum Doderlein, 1905. Zool. Anz. XXVIII, p. 621. 1906. Ech. d. 

 deutschen Tiefsee-Exp., Pis. XV, figs. 3, 3a ; XXXVIII, figs. 4a-h. 



Gulf of Aden ; 816 fathoms. 



In addition to the characters given above, this species has an unusual 

 number of abactinal ambulacral plates, in comparison with the number of 

 abactinal interambulacral plates. Thus, in Dbderlein's larger specimen 

 (55 mm. h. d.) there are 17 ambulacral and 10 interambulacral plates abac- 

 tinally, while in placenta of the same size there are 10-15 and 7-11 respec- 

 tively ; in adenicum, the abactinal interambulacral plates are less than .60 

 of the ambulacral, while in placenta they are .70— .75. Possibly the color may 

 be a good specific character, for Doderlein says his specimens appear to have 

 been dark red. 



