58 BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



or bluntly bi- or tri-tlcntate at tip; those of upper series shorter, more irregular, 

 often flattoncil, and apparcntl^y composed of two fused tubercles; sometimes two 

 subequal or very unequal tubercles stand side by side at upper end of plate. On 

 first plate three tubercles (shaped something like molar teeth) stand in a transverse 

 row at upper end of plate, and below them two or three short conical spines, the 

 lowermost in lino with the lower longitudinal series. Scarcely two proximal plates 

 are alike in armature. The opposite extreme is found in a large specimen from 

 off San Pedro in whicii there is an inconspicuous tubercle at the upper end of a 

 few of the proximal plates, the rest being unarmed. Any number of intermediate 

 forms may be found between these extremes. General surface of plates covered with 

 spinelets, which are flat, roundish, or polygonal and granuliform on the abactinal 

 surface of ray, becoming slender and capillary in the fasciolar grooves and toward 

 lower edge of plate. 



Inferomarginals extending laterally slightly beyond superomarginals, or not 

 at all. i\jmature consisting of about three or four tapering, slender, sharp, slightly 

 flattened spines in an oblique series on outer end of plate, and two or three shorter, 

 sharp, lanceolate spines on the aboral edge of the actinal surface of each plate. 

 Numerous shorter, lanceolate or blunt spinules usually accompany the regular 

 series. The actinal spines are broader, flatter, and more blade-like in some speci- 

 mens than others and the larger lateral spines vary considerably in length in pro- 

 portion to width of ray (one-fifth to one-half width), while some are slenderer 

 and less obviou.sly flattened than others. General surface of plates is covered with 

 flattened, round-tipped, squamiform spinelets. 



Adambulacral plates with an angular furrow margin. Furrow spines three, 

 of the usual astropectinoid t}-pe; central spine slightly longer than the two laterals, 

 compressed, blunt; lateral spines of series flattened, tapering, blunt. On actinal 

 surface, just behind furrow series, is a longitudinal series of two spines, the adoral 

 somewhat flattened, equal to or shorter than adjacent furrow spine; the aboral 

 spine greatly enlarged, subterete at base but much flattened beyond middle and 

 chisel-shaped or decidedly scoop-shaped at tip. In large specimens this spine 

 is 4 to 6 mm. long and 2 mm. broad at tip. Outside of this series, three or four 

 flattened spines, about equal to adoral member of above series in length, form 

 an oblique, irregular, or a longitudinal row, or a group. Sometimes at base of ray 

 tlie aboral member of the outer series is also enlarged, but it never attains the size 

 of the large spine. The great size of the enlarged spine often pushes the adoral 

 member out of place, usually toward the furrow. 



Mouth plates prominent actinally and rather narrow. Armature variable. 

 In large specimens there is usually a single series of prominent, blunt, or truncate, 

 flat si)ines parallel with suture between the two plates and increasing in size toward 

 the inner end of plate. On free margin of plate is an irregular series of much 

 smaller spines, and between the two numerous very short subcorneal spinelets. 

 Sr)metimes a second superficial series, smaller than the regular one, closely paraUels 

 It. The first adambulacral plate is much compressed and bears two closely appressed 

 transverse series of truncate spines, fanly regular in small examples, but irregular 

 m large. 



