676 PROCEEDINGS OF THE NATION AL MUSEUM. vol. xxxvi. 



There is sometimes a slight constriction about the basals or radials, 

 but more commonly none. The basals are separated by distinct 

 sutures. 



Stem in large specimens 190 mm. to 280 mm. in length, compara- 

 tively slender, with 74 to 10(5 joints, the* longest of which are 1.6 to 

 twice as long as broad, about 3 mm. long. The columnars are all 

 approximately cylindrical, those in the proxim.al third showing a 

 very slight tendency toward a barrel-like shape, the remainder to a 

 slight central constriction, but neither is as marked as in the related 

 species ; the lowest 30 mm. or 40 jnm. of the stem has the articulations 

 more or less swollen and produced, this soon giving place to numer- 

 ous fine radicular cirri and stout irregular branching roots. 



Type-specimen.~Cat. No. 22680, U.S.N.M., from Albatross station 

 No. 2401 ; Gulf of Mexico, off Pensacola, Fla. ; lat. 28° 38' 30'' N., 

 long. 85° 52' 30" W.; 142 fathoms; green mud and broken shell. 



R. 7'mrsonii may be at once distinguished from any of the above 

 species by its almost cylindrical c«lyx, Avhich is twice as long as 

 broad at the radials, the latter dimension being usually less than half 

 again as great as the diameter of the proximal part of the stem. 



The calyx of R. fcirfaHi (which is a perfectly valid species) is 

 more inclined to conical in its shape; the diameter across the radials 

 is .twice that across the distal end of the basals, while the length is 

 one and one-half times the breadth at the radials." 



Tlie species of Rhizocrinus may be conveniently grouped as 

 follows : 

 • (1) Basals anchylosed, without sutures: R. /ofofensis, R. rerrilli. 



(2) Basals always separated by distinct sutures. 



(«) Stem comparatively slender, the longer columnars being at 

 least twice as long as broad; calyx distinctly conical: R. conifer.^ 

 R. brevis, R. robvsfi/s, R. ehvni. 



(b) Stem very stout, the longer columnars but little longer than 

 broad; calyx approaching the cylindrical: R. rawsoni, R. farfaiti^ 

 R. wcheri^ R. saba\ 



Doderlein has found that the species of Bathycrinvs are, like the 

 species of Rhizocrinus^ divisible into two groups, one with the basals 

 anchylosed into a solid basal c\\\) or ring, the other with the basals 

 separated by suture. This was, however, known long ago, for Per- 

 rier's Ilyormias rec\('peratus is a species belonging to the latter group, 

 and was the first si)ecies of it to be described. A very good figure 

 of it was published by Perrier in his Explorations sous-marines, page 

 273, figure 193 (1886). 



« The data are taken from tbe figure published by Professor Perrier in lais 

 Exploi-ations sous-uiarines (1SS6). 



