ACTINOCRINID^. 627 



same order, which become free arm plates at the margin of tlie rim. The 

 various series thus formed are in contact laterally, and united by suture with 

 each other ; those of adjoining rays, as well as those of the same ray, forming 

 together the peculiar rim which surrounds the calyx at the brachial zone. 

 The plates of the rim are of nearly the same size ; they form longitudinal, 

 angular ridges, and from the outer end of each ridge proceeds an arm. Arm 

 openings large, all with a small respiratory pore at one side. Arms very 

 numerous, moderately long, simple, closely crowded together, and I'ather 

 small in proportion to the large size of the calyx. The pinnules, so far as 

 observed, provided with well defined hooks. Interbrachials numerous, separ- 

 ated from the interambulacral plates by the higher orders of brachials, 

 generally from the palmars up. Interdistichals one or two. Ventral disk 

 convex, in form of a ten-rayed star, slightly plicated near the outer margins, 

 and composed of a large number of plates, which decrease in size outward. 

 The orals, although well defined in young specimens, can scarcely ever be 

 identified in older ones. The inner floor of the tegmen is strengthened by 

 braces, which increase in thickness as they recede from the centre, and on 

 approaching the rim form tunneled passages for the recep)tion of the ambu- 

 lacra. The ambulacra follow the inner floor of the disk, being placed at 

 a slight distance from it ; they are roofed over wholly or in part by super- 

 imposed interambulacral jjieces, which, together with the radial dome plates, 

 if present, form a rigid and independent covering above the food grooves. 

 Column covered with rows of angular processes, passing up and down its 

 sides at equal distances, giving to the column a highly sculptured, angular 

 appearance, especially in its upper portions, where these processes are more 

 prominent, and in almost continuous vertical lines. They pass out from the 

 nodal joints, but intrude upon the intervening smaller ones, and grow farther 

 apart with the increase of internodal joints. 



Distribution. — This genus, like other extravagant forms, has a very 

 limited geological and geographical range, being restricted, so far as known, 

 to the Burlington group of the Mississippi Valley. 



Ti/pe of the genus : Teleiocrinus unibrosus Hall. 



Remarks. — We have called Teleiocrinus " a modified and extravagant 

 form of Cactocrinus " .• nevertheless we regard it as a good genus. It is 

 evidently the lineal successor of that genus in the Upper Burlington lime- 

 stone, having the same mode of bifurcation of the higher brachials, and other 

 general similarities. Cactocrinus flourished abundantly in the Lower Burling- 



