80 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



and prophetic of Promo palseaster in the conspicuous ambulacra! 

 furrows. 



Eays long and slender, elongate-petaloid, disk small. R = about 

 14 mm., r=4 mm. 



The interbrachial areas each have but a single, large, finely granu- 

 lated, axillary plate that margins the axils, and in tliis agree best with 

 Hudsonaster, but the rest of the known skeleton is that of 2Ieso- 

 palseaster. In the former genus the ambulacral fun-ows are always 

 very nan-ow and the ambulacraha are rarely seen, while in M. 

 intermedius the furrows are wide and the ossicles are rather like those 

 of Promopalseaster, though the same kind of ambulacraha is also 

 known in Mesopalseaster. Orad to the axillary plates there were two 

 small oral armature pieces that belong to the adambulacral columns. 

 These are not now present in the specimen, but the distinct and 

 large facet of the proximal side of the axillaries leaves no doubt on 

 this construction. 



Inframarginal columns well-developed proximally, though never 

 very prominent, and becoming rapidly smaller distally. The four 

 proximal pieces are the largest, beyond wliich there are at least 

 14 other ossicles, and all are closely in contact and alternate with the 

 adambulacrals. Another feature of these inframarginals is that not 

 more than six can be seen from the actinal surface, while the rest pass 

 on to the sides and distally even somewhat over to the abactinal 

 area. All of the plates are fuiely granulated. 



Adambulacral columns the most prominent of the actinal skeleton, 

 margining the distal half of the rays, and in the proximal portion 

 pass more and more inside of the inframarginals, diminisliing slowly 

 in size and finally depressed beneath the axillaries. There are 22 

 plates in a column, all more coarsely granulated than the inframar- 

 ginals, largest and most transverse near mid-length of the rays, and 

 all are drawn out inwardly into blunt points that adjoin the liigh 

 ridges of the ambulacraha. Therefore the adambulacral and the 

 adjacent ambulacral columns have the ossicles directly opposite one 

 another, but the adjacent ambulacral rows are shghtly alternating. 



Ambulacral furrows conspicuous and wide, widest in the proximal 

 third but converging somewhat quickly in the mouth area and far 

 more gradually distally. Therefore the furrows are elongate-petaloid 

 in shape. There are about 20 ambulacraha in a column. Proximally 

 the columns unite around and beneath the small adambulacral oral 

 armature pieces. Ambulacraha square to transversely rectangular, 

 each with a high L-shaped crest that laterally adjoins the points of 

 the adambulacrals and medially bends orally. Podial openings large 

 between the corners of pairs of ambulacrals and adambulacrals. 

 There is a well-developed groove down the center of the ambulacral 

 furrows. 



