138 



Bulletin, Vanderbilt Marine Museum, Vol. IV 



and extend to the anal system. The genital ring is narrow, the madre- 

 poric genital larger than the others. There are a few large secondaries 

 on the genital and ocular plates near the anal system and also addi- 

 tional tubercles on the madreporic genital. The poriferous zone is a 

 little sunken, the pores usually arranged in very regular arcs — vary- 

 ing with age from four to six pairs. The actinostome is small, the 



Text fig. 4. 



-Sphaerechinus granulans (Lamarck). A. Tridentate pedicellaria. 

 B. Globiferous pedicellaria, X 50. 



actinal cuts deep. The tubercles are a little smaller in the ambulacral 

 zone than in the interambulacral zone and are arranged in two to 

 four regular vertical rows, with an irregular median vertical line, 

 also with very small secondary tubercles placed between adjacent arcs 

 of pores along the entire poriferous line. In the interambulacral zone 

 the vertical rows of closely packed primary tubercles are also simul- 

 taneously arranged in regular horizontal rows, separated by vertical 

 and horizontal lines of secondaries and miliaries forming irregular 

 rectangles. The globiferous pedicellariae have rather short valves, 

 while the tridentate pedicellariae have somewhat broad, leaf-shaped 

 valves. 



