122 



ROBERT TRACY JACKSON ON ECHINI. 



m 



Text-figs. 118-122. — Ocular plate arrangement of Toxopmuslcs(itla?ilicus (A. Agassiz). Berniiid;i. .\I1 figures X 2.7. 



118. Diam. 51 mm. R. T. J. Coll., 873. All oculars exsert, extreme arrested variant. 



119. Diam. 77 mm. R. T. ,J. Coll., 893. Ocular I only insert., arrested variant, the largest specimen of the species 

 seen. 



120. Diam. 70 mm. R. T. J. Coll., 875. Oculars I, V insert, the typical character. 



121. Diam. 65 mm. R. T. J. Coll., 870. Oculars I, V, IV' insert, a common progressive variant. 



122. Diam. 59 mm. R. T. J. Coll., 877. Oculars I, V, IV, II insert, extreme progressive variant (p. 170). 



In the next larger series of Toxopneustes atlanticus, 45 to 60 mm. in diameter (1,463 speci- 

 mens), 67% have oculars I, V insert, a wide departure from variegatus. Of arrested variants 

 (one specimen) 0.1 % have all oculars exsert (text-fig. 1 18), 0.5 % ocular I only insert, and 0.1 % 

 have V only insert. As progressive variants, 28% have oculars I, V, IV insert and 1.2% have 

 I, V, IV, II insert (text-fig. 122), the extreme variation of the species as far as known. Aberrant 

 variants in this size are frequent, 36 specimens, or 2.5 %. Of these, ten specimens have oculars 

 V, II insert, fourteen have I, V, II, eleven V, IV, II, and one I, V, IV, III, this last a rare 

 variant in the family. 



In the largest series studied, 60 to 77 mm. in diameter (593 specimens), 68% have the 

 typical character of oculars I, V insert (text-fig. 120)*. Of arrested variants, 0.7% have ocular 

 I alone insert, one of these (text-fig. 119) being the largest specimen seen in the species. As 

 progressive variants, 29% have oculars I, V, IV insert and 0.7% I, V, IV, II insert. The 

 aberrant variants in this largest size are eleven, 1.8%; of these, four have oculars V, II insert, 

 five I, V, II, one V, IV, II, and one I, V, III insert, this last an extremely rare variant in Echini. 

 Looking at the tabulation as a whole (p. 161), it is seen in this species that the series 35 to 

 45 mm. iu diameter is not fully developed as shown by the percentages of progressive variants, 

 and aberrant variants are not quite so frequent as in the next larger size. In the series 45 to 

 60 mm. in diameter the range of percentages is practically the same as in the largest size, but 



