g2 BULLETIN '6, UNITED STATES NATIONAL MUSEUM. 



biliel. Rarely a second spinule accompanies the enlarged spine, or none of the 

 spiuelets may be flattened or furrowed, but tapering and fairly sharp, in which 

 case none of the marginal spines are flattened and bifid. Some (northern) speci- 

 mens have the enlarged "spine" very inconspicuous and only slightly larger than 

 the other spinelets. In small specimens there are but two or three actinal spine- 

 lets in addition to the spinule. Adanibulacral armature is extremely variable, 

 both according to size and locality. 



Mouth plates elongate, narrow, prominent actinally; interradial length 1.3 mm.; 

 width of combined j)lates .5 mm. At inner angle of combined plates are two stout 

 eidarged, somewhat curved, blunt spines, and the whole surface of the plates is 

 covered with short thick, blunt, very robust spinelets, which are largest near the 

 imier angle and decrease in size and tJiickness toward the margin adjacent to first 

 adanibulacral. Furrow series very angular, and consisting of a group of spinelets, 

 about six in number, situated at a higher level than the tooth, and continued to 

 first adanibulacral along the excavated short free margin in about four more short 

 pointed sj)inelets. The two actinal spines adjacent to teeth may be nearly as 

 large as the latter, making four teeth at angle, and one of the true furrow spinelets 

 is occasionally enlarged. In some specimens there is a regidar and prominent series 

 or double series along the margin of the median suture, with a few slenderer spine- 

 lets along the sides, lower down, the actinal surface of plates being very convex. 

 The first adanibulacral forms a short but wide companion plate, being much com- 

 pressed. 



Actinal interradial areas rather small; intermediate plates small on rays, 

 larger on disk, extending in a single series 0.75 to 0.8 length of ray measured along 

 side; a second series extends 0.5 to 0.6 as far as first; a third about 0.25 to 0.33 

 as far as the second (to the third to sixth inferomarginal). Large specimens have 

 seven or eight plates in an interradial series opposite first inferomarginal. Super- 

 ficially the plates appear roundish and much as in Psilaster, BatJiyhiaster, and 

 allied forms. Viewed from the inner side, the plates are seen to imbricate slightly, 

 and are a trifle tumid and armed with a group of rather delicate, often flattened, 

 obtuse, grooved, occasional!}- bifiil spinelets, similar near adanibulacral plates to 

 their outer actinal spinelets, and forming thence all the transitions between these 

 and the lower spinelets of the inferomarginals. These spinelets are all sheathed in 

 membrane, which is frecjuentl}' swollen at the tip; in some specimens the spinelets 

 have a papilliform appearance, and the calcareous part is slender and neetUe-like 

 without flattening or grooving. Not infrequently a central spinelet is enlarged, 

 and on some of the plates near the adambulacrals four or five spinelets form a 

 circular group, suggesting a sort of pedicellarian apparatus. 



Madreporic body large (7 nun. in diameter), entirely imcovered, circular to 

 irregularly oval, the inner edge being about at the midddle of minor radius. 



Color in hfe, madder brown. 



Anatomical notes.— Yevy well developed superambulacral ossicles are present; 

 these are absent from first four plates and rudimentary near tip of ray. The gonads 

 are not confined to the interradial region but extend a slight distance along ray, 

 there being ten to twelve independent clusters of tubules depending from each side 



