OCULAR AND GENITAL PLATES. 



115 



when only 100 were counted. Of course the rarer variants are usually found in only large 

 series, and one cannot know whether they are rare or not without having examined large num- 

 bers. A series of 229 specimens of Arbacia pundulata from Florida is interesting for compari- 



f12 



Text-figs. 111-114, — Oeular plate arrangement in Arbacia puiicliilala (Lamarck). WooiLs Hole, Massachusetts. 

 All figures X 3 (p. 175). 



111. Diam. 31 mm. R. T. J. Coll., 681. All oculars exsert, typical character. 



112. Diam. 42 mm. R. T. J. Coll., 682. Ocular V insert. 



113. Diam. 31 mm. R. T. J. Coll., 683. Oculars V, I insert. 



114. Diam, 38 mm. R. T. J. Coll., 684. Oculars V, I, IV insert. Figures 112 to 114 are all progressive variants. 



son with those from the northern locality. In the Florida series, 76 % have all oculars exsert, 

 19% have V alone insert, 2% have V, 1 and 1 % have V, I, IV insert; 3% have an aberrant 

 arrangement, one specimen having ocular IV only insert, and five having V, IV insert. In 

 comparing this with the northern form, best seen by the table (p. 158), it is obvious that the 

 Florida form is markedly more progressive in ocular arrangement than the northern. Also 

 in this respect it makes a closer approach to the character of the species occurring off the west 

 coast of South America. A similar difference seen in the character of a species from different 

 localities is shown also in several other species covering the commoner families of regular Echini. 



Of the rare species Arbacia dufresnii, 67 specimens are listed in the table. Some others 

 studied were omitted as too immature for the present consideration. The specimens are largely 

 horn San Antonio, East Patagonia, in the de Loriol collection at Geneva. In 87 % all oculars 

 are exsert as the species character. As progressive variants, in 4 % ocular V is insert, and in 1 % 

 oculars V, I are insert. Aberrant variants are quite frequent, 7%, as in other South American 

 species of the genus. Of these aberrants, two have ocular IV alone insert, and three have 

 oculars V, IV insert, I, II, III exsert. This last is a relatively frequent aberrant variation in 

 this genus. Eighteen specimens in the de Loriol collection which are considered too immature 

 for tabulation have all the oculars broadly exsert. Of the specimens studied, most have the 

 four periproctal plates characteristic of the genus; but two have three periproctal plates, four 

 have five, two have six, and one has nine periproctal plates (compare text-figs. 200-205, p. 175). 



Of the South American Arbacia spatuligcra (76 specimens) in only 9 % are the oculars all 



