114 



ROBERT TRACY JACKSON ON ECHINI. 



In Arbacia stellata (78 specimens) the oculars are typically all exsert, 95%. In three 

 specimens, 4 %, V is insert as a progressive variant, and in 1 % oculars V, I, IV are insert. 

 This, although southern, on the basis of ocular plates, is the most primitive of the living species. 



TEXT-FKiS. 107-110- 



107. Diam. 02 mm. 



108. Diam. 88 mm. 



109. Diam. 74 mm. 



■ Ocular arrangement in Slomopnnislcs rariolaris (Lamarck). Cej'lon. 

 R. T. J. Coll., 858. X 3. Ocular I only insert, an arrested variant. 

 R. T. J. Coll., 859. X 3. Oculars I, V insert, typical character. 

 R. T. J. Coll., 860. X 3. Oculars I, V, IV insert, a progressive variant. 



110. Diam. 86 mm. R. T. J. Coll., 861. X 3. Oculars I, V, II insert, an aberrant variant (p. 93). 



Arbacia lixula (141 specimens) has 94% with oculars all exsert, the typical character; 

 6 % are progressive variants, with V insert, and one specimen is aberrant with ocular IV alone 

 insert, a very rare variant in Echini. 



Of Arbacia punctulata I was fortunate enough, through the kindness of the Woods Hole 

 Biological Laboratory and other sources, to examine 2,100 specimens from Woods Hole, Massa- 

 chusetts. In this species typically, 87%, all oculars are exsert (text-fig. 111). As progressive 

 variants, 11% have ocular V insert (text-fig. 112). Only two specimens, 0.1%, have ocular 

 I alone insert. In 0.3% V and I are insert (text-fig. 113), and in 0.4% V, I, IV are insert (text- 

 fig. 114). This range of characters covers essentially the same series as seen in Arbacia nigra, 

 the most progressive species of the genus; but the relative frequency of characters is radically 

 different. In 0.6 % of the Woods Hole specimens the arrangement is aberrant. In nine out 

 of the twelve aberrants found, the arrangement is V, IV alone insert, which is a quite common 

 variant in this genus (see table, p. 164), but rare in other genera. One specimen has ocular IV 

 alone insert, a very rare character, one has I, IV and one has I, III insert, the last a unique 

 variant. 



Arbacia -punctulata, from Woods Hole, is distinctly more progressive in character than the 

 two previous species. It is worth noting that in this species, as in most studied, the character 

 was gathered from the first few examined and the commoner variants came along with great 

 regularity, so that the percentages in 2,100 specimens vary very slightly from \\hat thej- were 



