ACTINOCEINIDJE. 605 



Cactoerinus reticulatus (Hall). 

 Plate L VIII. Figs. Sa, h. 



1S61. Actiiiocriiim reticulatus — Hall; Descr. New Spec, of Crin. (prelim, notice), p. 2, and Boston 



Journ. Nat. Hist., p. 269. 

 18S1. Actinocrinis relktdatus — W. and Sp. ; Revision Palaeocv., Part II., p. 145. 



Syn. A. thoas Hall ; 1861, Descr. New Sp. Crin, (prelim, notice), p. 11. 



Sjn. A. locellus Hall; 1861, ibid., p. 15. 



Nearly as large as the preceding species. Calyx sub-ovate ; the dorsal 

 cup a little higher than the ventral disk, obconical, spreading uniformly to 

 the top of the distichals, thence abruptly to the arm bases ; the plates con- 

 vex, and ornamented as in C. prohoscidalis. Basal cup trilobate, short, thick- 

 ened at the lower margin, and projecting downward over the top of the 

 column ; interbasal sutures deeply grooved. Radials and costals decreasing 

 in size upwards, the radials nearly twice as large as the second costals. Dis- 

 tichals and palmars in single rows, the latter projecting outward. Arms four 

 to the ray, except in the two posterior ones, in which the palmars next to 

 the anal side support two post-palmars, giving to these rays five arms, or 

 twenty-two to the species. Arm facets large, subovate. Arms long, heavy, 

 and but very slightly tapering; they are cjdindrical in the lower portions, but 

 flatten toward the tips, and are composed of two series of moderately long 

 pieces, united by parallel sutures, and bordered by four longitudinal rows of 

 sharp nodes, two of them occupying the sides, the two others the back. 

 Regular interbrachials : 1, 2, 2, 1 ; the last, which rests between the pal- 

 mars, sometimes unrepresented. Anal plate followed by 2, 3, 2 and 1 plate, 

 the upper one separating the post-palmars. Ventral disk sub-conical, cov- 

 ered with well defined spines, irregularly arranged, some of them bi- and 

 tri-partite, separated by smaller convex pieces. Anal tube central or nearly 

 so, of moderate size, its length unknown. Column of medium size, composed 

 near the calj'x of alternate thick and thin joints, the former with undulating 

 edges ; axial canal rather large and pentangular. 



Sorison and Locality. — Lower Burlington limestone ; Burlington, Iowa. 



Tijjpe in the University Museum at Ann Arbor. 



Eetnarlis. — This species is readily recognized by its arm formula, its 

 heavy and spine-bearing arms, and by the spinous plates of the ventral disk. 



Under the name Actinocrinus locellus, Hall redescribed this species without 

 the tegmen, and under A. thoas a specimen with the arms attached. 



