244 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 8 



the primary spines; in young Centrechinus the spines are banded bluish 

 or purplish and white, in Centrostephanus dull purplish brown and light 

 yellow. With increasing age and size, the colors become duller until the 

 mature primaries are uniformly black in Centrechinus, dark brown in 

 Centrostephanus. It is unusual for banded spines to be evident in adults of 

 either genus but carefully preserved alcoholic specimens of Centro- 

 stephanus, even when full grown, commonly show the banding on some 

 primaries at least, though faintly. Most dry specimens, however, appear 

 to be more or less uniformly dark brown or quite black. On the contrary, 

 very young specimens (less than 10 mm in diameter) are unusually pretty 

 objects, the test and small spines deep brown, the dull yellow primaries 

 more or less evidently banded with purplish brown, and five or more 

 claviform spinelets, with bright rose-purple tips around the apical system. 



Distribution. — This species of Centrostephanus is definitely a shallow 

 water Mexican sea-urchin but the Velero took it at five stations in the 

 Galapagos Islands. At Albemarle Island it was found in shallow water 

 but ofif James Island it occurred in 36-60 fms. It was not met with at 

 either Cocos or the more northern islands (Socorro and Clarion), or on 

 the west coast of Lower California. Yet it is frequently found at Newport 

 and Corona del Mar, California, near low water mark. It has yet to be 

 taken on the mainland coast south of the Gulf of California but in the 

 Gulf it has been found as far north as Rocky Point, Sonora, and Consag 

 Rock, in depths down to 45 fms. 



Type. — Peabody Museum, Yale University, no. 964. 



Type locality. — Cape San Lucas, Lower California. 



Depth. — Shore to 60 fms. 



Specimens examined. — 131 specimens from 37 stations. 



Family Arbaciidae 



Arbacia incisa (Blainville;? Gmelin) 

 Plate 40, Fig. 11 



Echinocidaris incisa A. Agassiz, 1863, p. 20. 



Arbacia incisa H. L. Clark, 1913, p. 220. 



Arbacia stellata Mortensen, 1935, p. 575, pi. 70, figs. 6-9. 



This is one of the commonest sea-urchins of the Gulf of California 

 and was taken by the Velero at many stations there. Along the coast 

 southward it seems to be less common and relatively few specimens were 

 secured but unmistakable examples were collected as far south as Peru. 

 Indeed one of the largest specimens in the collection, 47 mm h.d., was 

 taken nine miles south of Zorritos Light, in shore collecting; from tip to 



