Verrill, Notes on Radiata. 

 Boletia picta Verriii. 



Psammechinus pidus Verrill, these Trans., p. 301, (young). 



Lytechinus semituberculatus {pars) A. Agassiz, op. cit, p? 301, (non Yal. sp.). 



Capt. Peclersen sent one large specimen of this species from La 

 Paz. It has but few spines remaining and the actinal membrane 

 is wanting. 



Diameter 4-10 inches; height IvSO; diameter of abactinal area 

 1-30; depth of cuts -25; diameter of abactinal area "60; of anal 

 membrane -24 ; breadth of ambulacral zones at periphery -98 ; of 

 poriferous zones, -22; of interambulacral zones 1-55; length of 

 larger spines of upper surface -30 to -35 ; their diameter -05 to -06 of 

 an inch. 



The test is very thick and firm for this genus. The outline is some- 

 what pentagonal, with rounded sides, the ambulacra somewhat bulg- 

 ing, and toward the summit somewhat raised above the concave 

 interambulacra. The lower side is concave ; the upper surface de- 

 pressed, subconical, elevated at the center. 



The actinal cuts are deep, their interambulacral margin raised^ but 

 not projecting inward beyond the ends of the ambulacral zones. The 

 lower surface is covered by numerous, nearly uniform, large tubercles, 

 which form about eight interambulacral and four ambulacral rows ; 

 m the former the two inner rows terminate about half way to the 

 actinal area and are separated by a median region of some width, on 

 which there are several irregular rows of smaller tubercles. On the 

 upper side each of the zones bears two primary rows of large and con- 

 spicuous tubercles, which commence at the summit and extend to the 

 actinal area. In the interambulacra the interior secondary rows com- 

 mence at about the third or fourth plate, as small irregular tubercles 

 at first, becoming about as large as the primaries near the periphery, 

 and extending nearly to the actinal area ; the exterior secondary row 

 commences at about the sixth or seventh plate, their tubercles, very 

 small at first, equalling the primaries at the periphery and extending 

 to the actinal area outside of the cuts, where they become small again; 

 the interior ternary row commences at about the ninth or tenth plate, 

 and the tubercles equal the primaries at the margin, but cease at five or 

 six plates from the actinal area ; the external ternary rows commence 

 a little above the periphery and extend about half way to the actinal 

 area, alternating irregularly with the external secondaries, but not 

 equalling them in size ; these two rows border the poriferous zones, 

 except near the summit ; near the periphery there are also interior 

 quaternary rows of small tubercles imperfectly developed, and some 



