1881.] NATURAL SCIENCES OF PHILADELPHIA. 219 



divisions of the ra3'S were laterally connected, but the rim is not 

 continuous above the five primar}^ divisions of the ray. 



We have already noticed the presence of small plates inter- 

 polated between the radial portions of the rim, forming sunken 

 areas, and having altogether the appearance of accessory pieces 

 (PL XVIII, fig. I,/)).). A closer examination, however, shows a 

 marked regularity in their arrangement, and there can be little 

 doubt that they represent pinnules, given off alternatelj^ from 

 opposite sides, and soldered into the body walls together with 

 arm joints. This interpretation is confirmed b}' the allied genus 

 Steganocrinus, in which tlie corresponding parts, under more 

 favorable conditions, instead of forming a rim, remained free 

 (PI. XYIII, fig. 3). 



Steganocrinus Meek and Worthen is connected with the other 

 section of Actinocrinus — tj'pe of A. multiradiatus — in the same 

 manner as the A proboscidialis group with Teleiocrinus. In 

 A. multiradiatus and allied species, the third primary radial is bent 

 abrupt!}^ outward, its upper articulating faces which support the 

 higher radials being directed almost horizontally, thereby forming 

 the raj^sinto protuberant lobes, separated by wide and deep inter- 

 radial depressions ; contrary to A. proboscidialis, in which the 

 arms are more or less continuous, and the sides of the calyx 

 nearly straight up to the tertiary radials. We should have sepa- 

 rated the two sections upon these characters, at least subgeneri- 

 cally, if Miller, in establishing the genus Actinocrinus, had not 

 unfortunately chosen for the t3^pe a species which is intermediate 

 between the two, thus rendering it difficult to determine the 

 typical form. It is veiy evident that the structure of the rays of 

 A. multiradiatus did not admit the development of a rim like that 

 of Strotocrinus and Teleiocrinus, as even the most profuse growth 

 could not well have filled the break between the rays, and the 

 spaces between the arms within the ra}^ were amply sufficient to 

 afford them free motion. This we think furnishes a reason wh}^, 

 under similar conditi(ms, the arms and pinnules of this genus, 

 contvar}" to those of Teleiocrinus, remained free during life. 

 Steganocrinus and Teleiocrinus have very close affinities in their 

 structure. In both of them there are five main raj^s — a succession 

 of radials longitudinally arranged — which give ofl" arms alternately 

 and from opposite sides; but, while in Steganocrinus the plates of 

 the difi'erent order of radials are extended into free appendages, 



