70 HAWAIIAN AND OTHER PACIFIC ECHINI. 



Agassiz's and Desor's genus. So far as spines and pedicellariae go, Dendraster 

 is not to be distinguished from Echinarachnius, yet the primary spines have 

 a characteristic form, the tip (PL 125, figs. 4? 5) being somewhat swollen and 

 then abruptly flattened and pointed. Pedicellariae seem to be very scarce and 

 small ; the bidentate have rather more of an apophysis than those of Echinarach- 

 nius parma but less than those of E. 7nirabilis. The genus contains but one 

 species. 



Dendraster excentricus. 



Scutella excentrica Eschseholtz, 1S31. Zool. Atlas, 4, p. 19. 



Dendraster excentricus Agassiz and Dcsor, 1847. Ann. Sci. Nat., scr. 3, 7, p. 135. 



This sand-dollar, characteristic of the Pacific coast of North America from 

 Lower California to Alaska, was collected by the Albatross at the following 

 points : — 



Union Bay, Bayne Sound, British Columbia. 



Station 2835. Off Lower California, 26° 42' 30" N., 113° 34' 15" W., 

 5.5 fms. Gn. m. 



Twenty-six specimens. 



Echinodiscus. 



Leske, 177S. Add. ad Klein, p. 131. 

 Tj-pe, Echinodiscus bisperforalus, Leske, 1778. Add. ad Klein, p. 132. 



This genus is notable as the only one among the Scutellidae which has 

 retained ophicephalous pedicellariae; at least, it is the only genus in wliich I 

 have found them. They have three valves, as in all other Echini where they 

 are known, and show no special pecuharities ; the blade (PI. 125, fig. 12) is 

 well rounded and quite spiny. The tridentate pedicellariae show some differences 

 which will be mentioned under the different species. Primary spines with swollen 

 and asymmetrical tips. The disks of the pedicels contain calcareous rods, with 

 rounded knobs on the convex side; as in Echinarachnius, these rods lie, two in 

 each sucker, with their concave sides towards each other. 



Key to the Species of Echinodiscus. 



Posterior ambulacra each with a deep, narrow, marginal sht,the depth of whichmayequal 



or even exceed the length of the unpaired petal auritus. 



Posterior ambulacra each with a lunulc distal to petal. 



Antero-lateral petals httle if any longer than posterior; length of test usually exceeds 



its width; lunules short icriuissimus. 



