34 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



are several longitudinal rows of small plates, with scattered larger plates between 

 them. 



The ambulacral deposits in the pinnules consist, when present, of small and very 

 slender spicules. 



The color in alcohol is brown, varying from very dark to almost whitish. The 

 cirri may be of the same color as the arms but are usually lighter and often white, in 

 striking contrast to the arms. 



The ventral surface of the centrodorsal is deeply concave in a small, but adult, 

 individual, less deeply excavated in a larger specimen. The radial areas are moderately 

 concave, and are separated by low rounded ridges. The central cavity, as viewed 

 ventrally, is rather small and pentagonal, with rounded angles. From it 10 grooves 

 run out for about a third the distance to the edge, the outer ends of the radial grooves, 

 lying on the base of the interradial ridges, being pointed, and those of the midradial 

 grooves being rounded. The central cavity is small, about a third the diameter of the 

 centrodorsal, and extends downward for only about half its length. 



The articular faces of the radials are very low, twice as broad as high or even 

 broader, and lie at a very large angle with the dorsoventral axis. The dorsal ligament 

 fossa is very low. The muscular and interarticular ligament fossae of the two sides are 

 separated by a rounded median groove. The interarticular ligament fossae are low, 

 then- distal border making only a slight angle with the fulcral ridge and running either 

 slightly upward or slightly downward from the central structures. At the inner end 

 of the upper edge of the interarticular ligament fossa is a large thick circular boss that 

 lies hi the plane of the central canal and hence extends deep within the muscular fossa. 

 The muscular fossae are small and low, scarcely larger than the interarticular 

 ligament fossae. 



Although the radial articular faces are oligophreate rather than macrophreate 

 in their general structure, they do not resemble those of any other oligophreate genus. 



The rosette is highly developed, with large interradial "spout-like" processes that 

 extend upward at an angle of about 45 and terminate in a broadly thickened rim. 

 In the center of the rosette, between these, is a pentagonal area enclosing a narrowly 

 5-pointed elevation with a raised area at the base of each of the rays. The rosette is 

 not attached either to the radial pentagon or to the centrodorsal; after removal of the 

 radial pentagon it remains closing the cavity of the centrodorsal. 



Larva. The skeletal elements of the larva as found in the sacs on the pinnules 

 are as follows : 



There are five large orals, usually all in contact, though the two ventral are often 

 separated in the midventral line. The orals are stout and evenly curved, without 

 upturned edges. The plane of the circlet of orals is at right angles to that of the 

 terminal stem plate, and hi the smaller individuals the aboral edge of the oral circlet is 

 in contact with the border of the terminal stem plate. 



Just beneath the orals are five basals of approximately the same size and similar 

 in appearance. The basal circlet is usually widely open in the midventral line. In the 

 younger larvae the basals beneath the two ventral orals completely fill the space between 

 the orals and the terminal stem plate. 



At the summit of the column and beneath the middle of the dorsal oral is a shallow 

 5-lobed saucer about half again as broad as the column. This is the circlet of 

 underbasals, of which there are apparently three. 



