OCULAR AND GENITAL PLATES. 121 



The five species of Toxopneustes all have typically oculars I, V insert, but there is consid- 

 erable variation shown. Toxopneustes maculatus (five specimens) has 80 % with oculars 1, V 

 insert and 20 % with I only insert as an arrested variant. Toxopneustes pileolus in 38 specimens 

 has 92 % with oculars I, V insert and 8 % as arrested variants with I only insert. Toxopneustes 

 semituberculatus in 25 specimens has 96% with oculars I, V insert and 4% arrested with I only 

 insert, thus being more progressive than pileolus. The next two species show arrested variants, 

 but also progressive variants, and in an increasing degree. 



Toxopneustes variegatus, from the West Indies and Florida (1,043 specimens, all adults), 

 has as the species character 90% with oculars I, V insert (text-fig. 184, p. 165). As arrested 

 variants, 1 % have ocular I only insert, one specimen has V only insert. As progressive 

 variants, 8% have oculars I, V, IV insert and 0.2% have I, V, IV, II insert; 0.8% are 

 aberrant variants. Of the eight aberrant variants, two have oculars I, IV insert, V being 

 excluded by the fusion of genitals 4, 5 as in text-fig. 144, p. 134; one has oculars V, II insert, 

 I being excluded by the fusion of genitals 5, 1 as in text-fig. 146, p. 134; and five speci- 

 mens have oculars I, V, II insert as in text-fig. 145, p. 134, a right-handed equivalent of the 

 typical progressive variant I, V, IV. The comparison of this species with the next, which is 

 a close ally, is interesting. 



Toxopneustes atlanticus (A. Agassiz), from Bermuda, has been considered a synonym of 

 T. variegatus (Lamarck), but it is here considered a distinct species. In Toxopneustes atlanticus 

 the species character of oculars I, V insert is taken on early, as usual, but the number of pro- 

 gressive variants typical of adults is taken on at a later stage than in any other sea-urchin 

 studied. I have therefore divided the material into three series : the smallest, 35 to 45 mm. in 

 diameter, which is still developing; a larger series, 45 to 60 mm., which is developed as regards 

 ocular arrangement; and a third series, 60 to 77 mm. in diameter, which includes the largest 

 specimens seen (table, p. 161). In the smallest series, 35 to 45 mm. in diameter (587 speci- 

 mens), 81% have oculars I, V insert, a much higher percent than in adults. Of arrested 

 variants 0.9% have I only insert, a small proportion, showing that it is fully developed in this 

 respect. One specimen, 0.2%, has ocular V only insert. As progressive variants, 16% have 

 I, V, IV insert, about half the proportion of adults, and 0.3 % have I, V, IV, II insert, again 

 about half the proportion seen in large specimens. There are in this smallest series twelve 

 aberrant variants, 2%. Of these, one specimen has oculars I, IV insert, four have V, II, six 

 have I, V, II, and one hasV, IV, II insert. 



' Toxopneustes allaidicus was described as IJ^ileclmius allanticus by Mr. Agassiz (1803) on the basis of its slender spines. 

 The spines are long, slender, soft to the touch, and typically of deep violet color, although light violet or green spines oc- 

 casionally occur. In T. variegatus the spines are stout, rigid, and usually gray or green. The peristomal i)lates are smaller 

 than in variegatus; the color of the test is violet, not green or gray mottled as in variegatus. The arrangement of ocular plates 

 as regards insertness differs very much from variegatus, progressive variants being more numerous as here shown. These 

 comparative characters are constant in the large series of each species observed, ^^'hilc these two species are very close, it 

 seems reasonable to consider atlanticus as distinct. 



