ACXmOCEINID^. 603 



Cactocrinus lucina (Hall). 

 Plate LVI. Figs. 8,9. 



1861. Actinocnmis hcina — Hall ; Prelim. Descr. New Pateoz. Crin., p. 11. 

 1881. Actinocrinus lucina — W. and Sp. ; Revision Palaeocr., Part II., p. 144. 



Syn. Actinocrinus puteatus Kowley and Haee ; Kansas Citj Scient., July 1S91, p. 101, Plate 2, 

 Fig. 16. 



A small species. Calyx biturbinate ; the sides to the top of the costals 

 very slightly convex, the distichals somewhat spreading. Plates a very little 

 elevated, and covered with obscure radiating ridges. 



Basals quite small, barely projecting over the sides of the column ; the 

 suture lines distinctly grooved. Radials and anal plate very little larger 

 than the costals ; the latter twice as large as the distichals, which support 

 two arms, making four to the ray, with frequently an additional arm in each 

 of the posterior rays. Arms delicate, three to four times as long as the 

 height of the dorsal cup, uniserial to the fourth or fifth plate, flattening in 

 their upper portions, and somewhat wider at midway than at either ex- 

 tremity. The distichals apparently consist of two pieces forming a syzygy, 

 and another syzygy occurs between the first and second palmar, the lines of 

 union at both places being much more obscure than between the other 

 plates. The third, fourth, and occasionally the fifth palmar are long and 

 cuneate, all above arranged in double rows. The free arm plates are . 

 thickened at their upper edges, and the sides distinctly serrated. Inter- 

 brachials at the regular sides five to six, at the anal side nine to ten. 

 Ventral disk nearly as high as the dorsal cup, the plates very uniformly 

 subspinous. 



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

 and Louisiana, Mo. 



RemarJcs. — Hall described this species with five arms in the two posterior 

 rays. What is supposed to be the type specimen in the Museum of Com- 

 parative Zoology, and two others, show four arms in all five rays ; but in 

 others the posterior rays have five. The form is intermediate between 

 C. proboscidalis and C. reticulatus, differing from them in the smaller size of 

 the arms ; very probably it is a yo\;ng stage of the latter, and should be 

 made a synonym. 



