ECHINOSOMA HOPLACANTHA. 161 



tenue, and uraniis are good species, but the others herein recognized are 

 of less certain validity. The nine accepted species are to be distin- 

 guished from each other as follows : 



Tube-feet abactinally in three series ; valves of large tridentate pedi- 

 cellariae strongly involute at middle. 

 Abactinal ambulacral plates only two or three times as numerous 



as actinal ; abactinal spines small and numerous hoplacantha. 



Abactinal ambulacral plates four-seven times as numerous as acti- 

 nal; abactinal primaries long and conspicuous, secondaries and 



miliaries few liiculentum. 



Tube-feet abactinally in one or two series. 



Abactinal surface sparsely covered with spines, rarely more than 

 two primary or large secondary tubercles on a plate ; second- 

 aries and miliaries not abundant. 

 Abactinal coronal plates rather high, 11-14 in a specimen 125 mm. 



h. d.; tridentate pedicellariae with slightly involuted valves hispidum. 

 Abactinal coronal plates lower and more curved, 14-16 in speci- 

 mens 100-125 mm. h. d. ; valves of tridentate pedicellariae 



not involute at all tenue. 



Abactinal surface more or less thickly covered with spines, often 

 three or more large tubercles on a plate; secondaries and 

 miliaries often abundant. 

 Ambulacra distinctly broader than interambulacra. . . . Koehleri. 



Ambulacra not broader than interambulacra. 



Actinostome very large, exceeding .35 h. d., with deep buccal 



slits zealandice. 



Actinostome not so large, buccal slits slight. 



Whole test thickly tuberculated ; actinal primary tu- 

 bercles rather small, in vertical series of 6-8 extend- 

 ing nearly to actinostome panamense. 



Test not so thickly tuberculated ; actinal primary 

 tubercles in vertical series of 3-6, confined to 

 peripheral half of actinal surface. 

 Valves of tridentate pedicellariae rather flat, not 



involute near middle U7'anus, 



Valves of tridentate pedicellariae strongly involute 



at middle, and more or less curved Petersii. 



Echinosoma hoplacantha A. Ag. and Cl. 



PhortnoBoma hoplacantha Wyville Thomson, 1877. Voy. "Challenger," Atlantic, I, 



p. 148. 

 Phormosoma hoplacantha A. Agassiz, 1881. "Challenger " Ech., Pis. XI ; XII; Xlla, 



figs. 10-18. 

 Hygrosoma hoplacantha Mortensen, 1903. " Ingolf " Ech., I, p. 59. 



Pacific and Indian Oceans ; 402-1375 fathoms. 



This is not only one of the largest (312 mm. h. d.) of the EchinothuridoB, 



but it is one of the most easily recognized for the numerous, slender spines 



11 



