LECANOCRINIDAE 1 73 



Cholocrinus obesus (Angelin) 

 Plate IX, figs. 1-4 



Forbesiocrinus obesus Angelin, Icon. Crin. Sueciae, 1878, p. 9, pi. 21, fig. 18, not fig. 21, nor pi. 28, 



figs. 2, 3. 

 Lithocrinus obesus, Wachsmuth and Springer, Revision Palaeocrinoidea, pt. 1, 1879, p. 53. 

 Cholocrinus obesus, Springer, Jour. Geology, XIV, 1906, p. 515. 

 Forbesiocrinus divaricatus Angelin (in part), Icon. Crin. Sueciae, 1878, p. 9, pi. 26, figs. 6, 6a. 



Type of the genus. 



Specimens of moderate size. Crown elongate. Calyx well differentiated 

 from the arms, with wide interbrachial spaces; conical, truncate below, com- 

 posed of strong plates; spread of calyx from base to top of RR about i to 2.7; 

 height to width, 1 to 1.5. Surface smooth or coarsely wrinkled. Maximum 

 crown, 35 mm. high by 20 mm. wide; base, 8 mm. Column of small specimen, 

 20 mm. long. 



IBB large, erect, visible as pentagons and forming a conical ring wider than 

 column. BB large, about as wide as high. RA small ; anal x large, widening 

 upward with truncate and rounded distal margin. RR the largest plates in the 

 calyx, with shallow facets half to two-thirds the width of the plates. IBr short 

 and wide. Height of B to R to IBr, 3:3:1. IBr 2 to 5, the latter number appar- 

 ently in right posterior ray only. Rays unequal, the anterior and two pos- 

 terior greatly developed, the lateral small and relatively dwarfed; dividing into 

 two main branches which divide again in the three larger rays, giving off branch- 

 ing ramules at irregular intervals at either side of the dichotom ; ray divisions 

 rounded, long and heavy. The two smaller rays covered by the larger ones be- 

 yond the second bifurcation. Column short and stout, with expanded encrust- 

 ing root for attachment to other bodies ; prominent rounded columnals project 

 at irregular intervals for the greater part of its length, with several shorter and 

 narrower ones intervening. Tegmen composed of finely plated perisome, with 

 strong ambulacral plates. 



Among the irregularities in arm branching for which this species is notable may be men- 

 tioned a peculiar difference in the two posterior rays. In the right, a small ramule is given 

 off to the left (outer) side from IBr 2 , while the main division takes place two or three plates 

 beyond that ; in the left the main division is on IBr 2 as in the other rays, and the first outer 

 ramule is given off at about the fifth plate above. This is constant in the two specimens in 

 which these parts are well preserved. The figures are based upon four specimens already 

 mentioned in the remarks on the genus; they are new and original drawings by Mr. Liljevall 

 from Angelin's types, two specimens since found, and the fragment of F. divaricatus— all 

 from horizon (/) at Follingbo. Additional cleaning has brought out clearly the anal side in 

 the type specimen of C. obesus, in which the posterior basal, incorrectly drawn in Angelin's 

 figure 2 on his plate 28, is plainly seen with its curved suture next to the radianal (PI. IX, 

 fig. ic, and sketch id). 



Types. In the Riks Museum, Stockholm. 



Horizon and locality. Silurian, Wenlock Group, horizon f ; Follingbo, Island of Gotland. 



