110 PALaiONTOLOGY OF NEW-YORK. 



Mariuerinus plumosus (n. s.)- 



Plats III. Fig. G - 11. 

 Body small, obconic or turbinate : surface ornamented by strong radiating 

 ridges proceeding from the centre of the plates. Basal plates about as 

 long as wide. First radial plates a little longer than wide : second and 

 third radials scarcely longer than wide. Interradial plates one below, 

 succeeded by three ranges of two each. Radial and interradial plates 

 strongly marked by radiating ridges. Brachial plates two at the base, 

 which give origin to two ranges in direct line of three plates each 

 and an intercalated plate, which rests upon the contiguous sloping 

 edges of the two outer lower brachial plates; and above this, two 

 ranges of two small plates each, precisely as in the interradial plates. 

 From the summit of these originate four arms, composed of subcuneiform 

 plates with lateral tentacles originating from the thicker sides. Ten- 

 tacula near the base of each outer arm of the four, originating on every 

 second plate, and sometimes an interval of two plates without tenta- 

 cles ; while on the two inner arms there appear to be no tentacles till 

 about the eighth joint. Tentacula round, gradually tapering : joints 

 short. 

 Column round, comparatively large ; consisting, near the base of the 

 body, of nearly equal joints. 



This species, in the aspect and structure of the body, ornamenting of surface, etc. 

 scarcely diflFers, except in size, from M. pachydactylus. The arrangement of the 

 brachial joints, and the character of the arms, are most conspicuously distinct. 

 The first bifurcation of the brachial plates is, however, the same; but at the second 

 bifurcation, the lateral brachial plates sustain the outer arms, which correspond to 

 the auxiliary arms in the preceding species; while the upper ones of the central 

 range, together with the inner oblique edges of the outer ones, sustain two small 

 plates which give origin to the central pair of arms, corresponding to the main 

 arm of the preceding species, but which is here reduced to the condition and 

 structure of two of the armlets, and furnished in like manner wath tentacula. The 

 character of the species is thus most remarkably changed, by a modification of the 

 brachial arrangements, reducing the whole number of these appendages to four from 

 each ray, or twenty altogether; while in M. nobilismnus there are more than sixty 

 from each ray, and more than three himdred altogether. 



