1913.] Clark, Echinoderms from Lower California. 189 



time it is quite possible that all of these nominal species are really one. For 

 the present, I think it desirable to retain the names erinaccus and peruvianus 

 to distinguish the two forms now recognized, the former with spines on 

 the outer edge of marginal plates at middle of arm and the series double, if 

 anywhere, at base of arm; while the latter has the spines on the inner edge 

 of the plates and the series double, if anywhere, near tip of arm. 



The specimens in the present collection show interesting geographical 

 diversity. The specimens from Ballenas Bay and San Bartolome have 

 relatively broad arms, inconspicuous superomarginal spines in incomplete 

 series, central granules of paxillse noticeably enlarged and the stout actinal 

 spine on each adambulacral plate short and truncate; R = 85, r = 17 and 

 br = IS mm. or R = 62, r = 18 and br = 17 mm. So R = 3.5-5 r or br. 

 The color of these more northern specimens is light yellowish-brown. The 

 individuals from Cape St. Lucas are smaller, ranging from R = 8 to R = 

 55 mm. The latter has r and br scarcely more than 10 mm. so that the 

 rays appear longer and narrower than in the more northern specimens. 

 The color is also different; brown with a tinge of purple. The supero- 

 marginal spines are conspicuous and the series are quite complete, being 

 double near the bases of the arms, but not in the arm-angles. The central 

 granules of the paxillre are not enlarged and the big actinal spine on each 

 adambulacral plate is quite long and rounded at tip. These specimens 

 from Cape St. Lucas approach those in the M. C. Z. collection from Peru, 

 but the latter have the actinal spines on the adambulacral plates still 

 longer and more pointed and the spinelets of the paxilhe are not at all 

 graniform. In these particulars the difference between southern (Peru) 

 and northern (California) specimens is very marked but the Cape St. 

 Lucas specimens are intermediate. 



San Bartolome, west coast of Lower California. 



Ballenas Bay, west coast of Lower California. 



Cape St. Lucas, Lower California. 



Eight specimens. 



Psilaster pectinatus. 



Bathybiaster pectinatus Fisher, 1905. Bull. Bur. Fish., Vol. 24, p. 295. 

 Psilaster pectinatus Fisher, 1911. Bull. U. S. Nat. Mus., No. 76, p. 72. 



Both of the specimens before me are young (R = 13 and R = 35 mm.) 

 and show no characters worthy of mention. 



Station 5692. Off Pt. San Tomas, west coast of Lower California, 

 1076 fms. Bottom Temp., 37.1°. 



