1886.] NATURAL SCIENCES OF PHILADELPHIA. I4t 



Attelesocrinus delicatus, nov. sp 



Calyx bell-sbapecl ; twice as high as wide, greatly constricted 

 along the sutures between basals and underbasals. Underbasals 

 forming a comparatively long ovo-cjdindrical body. Basal cup 

 funnel-shaped, resting upon the underbasals as if proceeding from 

 their inner cavity. The basals are delicate plates, elongate, gradu- 

 ally increasing in width. Arm-bearing radials wider than high ; 

 each one supporting two brachials. The latter fill nearly the 

 entire width of the preceding plate, and are twice as wide as the 

 true arm plates. Anterior radial narrow, less than half the width 

 of the arm-bearing radials. Arms two to the ray, tapering 

 gradually to their tips, where they become extremely delicate; 

 they have a waving outline, are composed of long joints, and 

 give off armlets alternately from every second plate. All armlets 

 extend to the tips of the arms, and branch once or twice. Their 

 size along the lower part of the arms is only half that of the main 

 arms, but higher up they are of almost equal thickness. Column 

 obtusely pentangular. 



Geological Position^ etc. Lower Burlington limestone. Burling- 

 ton, Iowa. 



Atelestocrinus robustus, nov. sp., PI. 9, fig. 4. 



Larger and much more robust than the preceding species ; less 

 constricted between basals and underbasals ; the form of the 

 latter, taken together, more oblate. Basals twice as long as wide. 

 Arm-bearing radials heavy, wider than high ; the anterior radial 

 less than one-third the size of the others, hexagonal. Azygous 

 side with four plates in the calyx, two of them constituting parts 

 of the ventral tube ; alternately arranged. Brachials four ; three 

 of them quadrangular, the upper one axillarj^ ; all rather large, 

 but decreasing in size upwards. Arms long, comparativel}^ heavy 

 at the base, but tapering rapidl}^ to the tips, where they become 

 very delicate. They are composed of quadrangular, rounded 

 joints, with parallel sutures, giving off armlets alternately from 

 every second joint. The armlets are much thinner, and more 

 pinnule-like than in A. delicatus, but extend like those to the 

 height of the arms, and bifurcate in a similar manner. 



Geological Position, etc. Burlington and Keokuk Transition 

 bed near Burlington, Iowa, and at the base of the Keokuk 

 limestone, White's Creek Spring, near Nashville, Tennessee. 



