144 



ROBERT TRACY JACKSON ON ECHINI. 



pores and ocular I only is insert; an older, but still very young specimen, 22 mm. in diameter, 

 has the bivium insert, the species character. Of adults, 179 were examined, including a superb 

 series of 61 specimens from Friday Harbor, Puget Sound, Washington, kindly sent me by Mr. 

 A. P. Romine. Of this species, in 87 %, oculars I, V are insert (text-fig. 152). In 1 % ocular 

 I alone is insert as an arrested variant. Both of the two specimens showing this character are 

 adults, one being very large, 145 mm. in diameter (text-fig. 151). Of progressive variants 



n 



v 



152 



153 



TEXT-FIGS. 150-153. Ocular plate arrangement in Strongylocentrolus franciscanus A. Agassiz. 



150. Monterey Bay, California. Young. Diam. 5.5 mm. R. T. J. Coll., 552. X 6.5. Ocular I alone insert as a 

 developing character, no genital pores. 



151. Friday Harbor, Puget Sound, Washington. Diam. 145 mm. R. T. J. Coll., 906. X 1.6. Ocular I alone 

 insert, an arrested variant. 



152. California. Diam. 154 mm. R. T. J. Coll., 724. X 1.6. Oculars I, V insert, the typical character. An 

 exceptionally large specimen (text-figs. 166, p. 149; 199, p. 171). 



153. Vancouver, British Columbia. Diam. 126 mm. R. T. J. Coll., 725. X 1.6. Oculars I, V, IV insert, a progres- 

 sive variant. 



11 % have oculars I, V, IV insert. The specimen from which text-fig. 152 was drawn is ex- 

 ceptionally large, 154 mm. in diameter, the largest seen, yet it has only the bivium insert; 

 the progressive variants were all considerably smaller. One specimen only is aberrant with 

 oculars V, II insert, ocular I being excluded from the periproct by the fusion of genitals 5, 1 

 as in text-fig. 146. Of the three adults here figured it is noteworthy that the largest specimen 

 (text-fig. 152) has the smallest apical disc and the next smaller specimen, which is an arrested 

 variant (text-fig. 151), has the largest apical disc (p. 87). 



The most progressive species of the genus is Strongylocentrotus purpuratus from California. 

 Through the kindness of Dr. W. K. Fisher, I received a fine series of specimens; with 

 others, 120 have been studied. In this species 77 % have oculars I, V insert, 1 % is arrested 

 with I only insert, and 22 % are progressive variants with I, V, IV insert. The species eury- 

 throgrammus, franciscanus, and purpuratus, although they have oculars I, V insert as a typical 



