NO. 5 CLARK : ECHINI OF WARMER EASTERN PACIFIC 279 



Another remarkable thing affecting the color is undeniable hybridiza- 

 tion of franciscanus and purpuratus. The hybrids when young have the 

 primaries quite purple or bright violet and shades of these colors persist as 

 the animal grows. The hybrids are distinguishable from purpuratus by the 

 smaller number and much greater size of the primary spines, while their 

 unusual color distinguishes them from franciscanus. Of course, many speci- 

 mens are so nearly intermediate, their identification becomes a matter of 

 opinion. A careful study of this hybridization would surely be rewarding. 



Distribution. — There is no doubt that franciscanus is characteristic of 

 the coastal region of the western United States and Canada, and Morten- 

 sen reports its occurrence on the Alaskan coast and even in northern Japan. 

 How far south on the American coast its range extends is still somewhat 

 uncertain. Mortensen sa^'S Cedros Island, Lower California, is the south- 

 ern limit and two small specimens in the Velero collection from that island 

 and two from Thurloe Bay, near the island, confirm that opinion. There 

 is, however, in the present collection a very good adult specimen from 

 "shore collecting at Petatlan Bay, Mexico," Lat. 17° 31' 45", but this 

 seems quite improbable and needs confirmation. In the vicinity of Newport 

 and Balboa, California, franciscanus is common and grows to a large size, 

 but the largest specimens in the Velero collection are from shore collecting 

 between Cape Arago State Park and Yaquina Head Light on the Oregon 

 coast. 



Type.— M.C.Z. no. 1686 (Cotype). 



Type locality. — San Francisco, California. 



Depth. — Shore to 50 fms. 



Specimens examined. — 343 specimens from 24 stations. 



Strongylocentrotus purpuratus (Stimpson) 

 Plate 44, Fig. 22 



Echinus purpuratus Stimpson, 1857, p. 86; 1857a, p. 526. 

 Strongylocentrotus purpuratus A. Agassiz, 1872a, p. 165. 



Mortensen, 1943a, p. 236, pi. 26, figs. 1-8. 

 Like franciscanus, this species is characteristic of the western coast of 

 North America. It is even more common, the present collection contain- 

 ing over 500 specimens. They show a diversity in spinulation which is more 

 extraordinary than anything shown by any other American sea-urchin. 

 The normal condition is the presence of a double series of primary spines 

 in each ambulacrum and interambulacrum ; these spines are about 10 mm 

 long, rather stout and quite acute. Each ambulacral plate carries an addi- 

 tional primary spine, not so large at each end of the plate. Each inter- 



