AGASSIZ AND CLARK : REPORT ON ECHINI. 121 



markably long, low plates, which just above the ambitus are 25 mm. long and 

 only 5 mm. high. There are no primary tubercles above the ambitus but the 

 whole abactinal surface is rather closely covered with slender secondaries and 

 miliaries. On the actinal surface, primary spines are fairly numerous but show no 

 regular arrangement. Many ambulacral plates have two, and many interambu- 

 lacral plates four spines. The areolae are small, the diameter usually less than 

 half the height of the plate. The primary spines are seldom 25 mm. long and 

 terminate in a conspicuous white hoof; nearly all are, however, broken off. The 

 pedicellariae are interesting, for in addition to tridentate pedicellariae, similar to 

 those of Sperosoma biseriatum Dod., but seldom with valves as much as two milli- 

 meters long, we find ophicephalous and triphyllous pedicellariae abundant. The 

 latter are not peculiar but the former arc almost exactly like those figured by 

 Mortensen (1903, PI. 14, fig. 23) as characteristic of his proposed new genus 

 "Tromikosoma" ! In no other respect, however, does this species resemble that 

 group. Unfortunately only one specimen of this interesting Echinothurid was 

 taken. 



Station 5082. Off Omai Saki Light, Japan, 662 fathoms. 



One specimen. 



ECHINOMETRIDAE Gray. 



Strongylocentrotus Drobachiensis A. Ag. 



Echinus Drobachiensis O. F. Muller, 1776. Prod. Zool. Dan., p. 235. 

 Strong ijlocentrotus Drobachiensis A. Agassiz, 1872. Rev. Ech., Pt. 1, p. 162. 



A considerable number of specimens of Strongylocentrotus were collected along 

 the North American coast from British Columbia northwestward, across the 

 Pacific. They show little diversity among themselves and only very slight, if any, 

 differences from specimens collected at Eastport, Maine. Eor the present at 

 least they may be considered as Drobachiensis. 



Bayle Island, British Columbia. 



Unalaska, Aleut iau Islands. 



Atka, Aleutian Islands. 



Agattu, Aleutian Islands. 



Medni, Komandorski Islands. 



Bering, Komandorski Islands. 



Petropaulovsk, Siberia. 



Forty-three specimens. 



Strongylocentrotus nudus A. Ac. 



Toxocidaris nuda A. Agassiz, 1863. Proc. Acad. Nat. Sci., Phila., p. 356. 

 Strongylocentrotus nudus A. Agassiz, 1872. Rev. Ech., Pt. 1, p. 165. 



A single immature specimen, only 23 mm. in diameter, seems to be the young 

 of this species, for the arcs of 6 or 7 pairs of pores are nearly vertical and the 

 poriferous zones are correspondingly narrow. The primary tubercles are conspicu- 

 ous while the other tubercles are few in number and small. The abactinal ambu- 



