THE I'KHIPIKMT. 



175 



of these two, which appears to be the suranal, lies dorsal to genital 3, a* in Salenia. In Acro- 

 salenia wiltoni (text-fig. 105, p. Ill) there are four large periproeial plati- !> -ides a vacant 

 space, doubtless for small anal plates as in Salenia. The largest of these four is probably the 

 suranal and lies dorsal to ocular III, as in Acrosaknia spinosa and Peltastes. 



In Arbacia there are typically four plates in the periproct, but as variant- there may l>e 

 fewer or more than this number. Bell (1879) notes that there may l>e a> few a- thn< or an 

 many as ten, and Mr. Agassiz (1881, p. 57) notes that there may he more than four up to thir- 

 teen periproctal plates. I noted (1899, p. 131) that in Arbacia punctulala there may be as few 

 as three or as many as nine plates as variants from the typical four. In Arliaeia the typiral 

 four periproctal plates lie in such planes that two are in the antcro-posterior axis III, 5, and 

 two are on each side of this axis (text-figs. 111-114, p. 115; text-figs. 1G7, p. 149; 202). The 



m 



TEXT-PIGS. 200-206. Variation of periproctal plates in Arbacia with the typical rhanirtrr in II:ibrocidaris. 

 200. Arbacia punctulata (Lamarck). Woods Hole, Massachusetts. Diam. 25 mm. R. T. J. Coll.. 7J7. 

 Only two periproctal plates; suranal dorsal to genital 3. 



X3. 



201 

 202 

 203 

 204 

 205 

 205a. 



The same. Diam. 45 mm. R. T. J. Coll., 728. 



The same. Diam. 47 mm. R. T. J. Coll., 729. 



Diam. 31 mm. R. T. J. Coll., 730. 



Diam. 36mm. R. T. J. Coll., 731. 



Diam. 43 mm. R. T. J. Coll., 732. 



The same. 

 The same. 

 The same. 

 The same. 



X 3. Only throe periprortal plates. 



X 3. Four periprortal plali-s, tin- typiral character (p. 115.) 



X 3. Five ]x>riproctal plates; rompan- trxt-fiK.206. 



X 3. Six periproctal plates. 



X 3. Many prriproct:il platrs. 



a __.... Florida. Diam. 32 mm. R. T. J. Coll., 890. X 4. One large and about fifty small periprocUl 



P lateT""The7 P ~eci"men is so distorted its ocular arrangement is omitted in tabulation of il.- M-" '-. pp. 



206. Habrocidaris scutala (A. Agassiz). Santa Cruz, West Indies. Di,,m. 17.5 ,,,m. A,la P t,-l 

 Clark, 1908, Plate 54, fig. 5. X 3. Five periproctal plates; compare text-f, K . 21M. 

 pore in genital 2 (compare Plate 3, fig. 14). The genital pores lie very far dorsally (p. I.- 1 ) 



