OCULAR AND GENITAL I'LATKS. |j:, 



ing and a developed series. In the developing series of 55 specimens, varying fro.,, 19 to 60 

 mm. in diameter, 76% have the bivium insert, quite near to the character <.f adult, from lier- 

 muda. In 9% ocular I only is insert. Of progressive variants, 13% have oculars I, V, I\ 

 insert. This is much below the percentage of adults, in which I, \ . IV in-.-n ,- tin- character 

 in this region. One aberrant has oculars I, V, II insert. 



In the developed series of 50 to 127 mm. diameter from the \\V-t Indie.- ami Florida 

 specimens), in 38% oculars I, V, IV are insert as the typical character (tcxt-lig. H.Vi. Tin- 

 is the only species of the family in which I, V, IV has been found as a dominant character, 

 although it is a frequent variant in many species. As arrested variants two specimen*, large 

 adults, have V only insert. In 36% oculars I, V are insert (text-fig. 124). Thi- i- an arrested 

 variant for the southern, while it is the typical character for the Bermuda form of the SIXHJMB. 

 As progressive variants 18% have oculars I, V, IV, II insert (text-fig. n> n) . Thi- variant i* 

 important as it includes the bivium and posterior pair of the trivium, thus marking the bilateral 

 symmetry in regular Echini as indicated by the incoming of ocular plates. In 1',' all the 

 oculars are insert (text-fig. 127). The aberrant variants of the southern form of Tri/>nru*te* 

 esculentus are rather frequent, 6%. Of the 27 aberrants, one has oculars I. IV in-ert. a- in 

 text-fig. 144, and 24 have oculars I, V, II insert, which is the bivium and right posterior plate of 

 the trivium instead of the left as usual. One specimen has V, IV, II insert , in which ocular I 

 is excluded by the fusion of genitals 5, 1 (text-fig. 1%); and one ha- I, V, IV, III in-ert. a rare 

 variant in the order but common in the Cidaroida. The difference in TripneusU-* > M-I//< ///H* from 

 Bermuda and the West Indian area appears to be marked only in the arrangement of the ocular 

 plates, no other distinction being observed. It is the same difference noted in -everal other 

 species where series from widely separated areas are tabulated. It shows differential character- 

 developing, not distinguishable in a single specimen, but obvious in a large series. Such may l>e 

 considered as incipient species in the process of making. In the total number of 7(K5 specimens 

 tabulated, it is interesting to note that of 30 aberrants, 26 are cases of I, V, II insert, and of tin- 

 other four cases in three (p. 164) the aberration was due to the fusion of two uenitaU 

 mechanically shutting out an ocular. 



Of Evechinus chloroticus (20 specimens) in 90% oculars I, V are insert, one specimen is a 

 progressive variant with I, V, IV insert, and one specimen is aberrant with I, IV insert. 



Considering the family Echinidae as a whole, many species of the genus Kchinus have all 

 oculars exsert as a character. One species, Echinus magellanicus, has ocular I only in-ert. and 

 many species in the family have typically oculars I, V insert. Only one specie-. Tn/>nnutes 

 esculentus, has typically oculars I, V, IV insert and this only in its southern localities, 

 or five plates insert are rare in the family except in the southern form of Tn/>neustes csculrntu* 

 and the Antarctic species of Echinus (table, pp. 160, 161). 



The Strongylocentrotidae includes genera in which the test is circular in outline, with 



