254 PROCEEDINGS OP THE ACADEMY OP 



greatly extended out horizontally in the form of remarkably elongated, slender, 

 rigid, arm-like appendages, which are covered in above, all the way out, with 

 small pieces like these of the vault, and bear the true arms along their sides. 

 In some species, these long free rays are known to bifurcate once, while in 

 others they are simple all the way out, so that in the latter the radial pieces 

 may be said to continue indefinitely in a direct Hue. 



Type. SteganScrinus pentagonus, = (Actiriocrinus pe'ntagonus, Hall.) It 

 also includes Steganocrinus araneolus, = (Actinocrinus araneolus, M. & W.), 

 and S. sculptus=Aetinocrinus sculptus, Hall. 



Rhodocrinus nanus, M. & W. 



Body small, subglobose, with nearly vertical sides which round under below 

 to the basal concavity. Base very small, and entirely concealed in the concavity 

 of the under side, by the end of the column. Subradial pieces comparatively 

 large, forming the under side of the body, and curved up so as to show nearly 

 half the surface of each in a side view, hexagonal in general outline, but 

 probably each with a seventh nearly obsolete angle at the middle of the side 

 connecting with the base. First radials nearly as large as the subradials, and 

 regularly heptagonal in form ; second radials rather more than half as large as_ 

 the first, normally hexagonal, but sometimes pentagonal and rarely quad- 

 rangular ; third radials larger than the second, generally wider than long, 

 pentagonal, hexagonal or heptagonal, and' supporting upon their superior 

 sloping sides, apparenly the first brachial pieces, which are not free, but 

 supported by the first free pieces in the next range ; if there were no farther 

 divisions of the free rays, there must therefore have been two arms to 

 each ray, or ten in the entire series. First interradials smaller than the 

 first radials, and resting upon the truncated upper sides of the subradials, 

 regularly hexagonal in form, or rarely with the superior angle slightly trun- 

 cated by tlie middle piece of the next range, so as to form a seventh angle ; 

 second range consisting of two, or rarely three, rather smaller generally hex- 

 agonal pieces, above which there are five or six other still smaller pieces 

 connecting with i lie vault between the arm bases, thus making some eight or 

 nine interradials to each area ; anal pieces about the same number as 1 in each 

 interradial space, but a little larger in size and differently arranged, there 

 being three pieces in each of the ranges above the first one, the middle ones 

 of which continue on up in a right line to connect with the base of the 

 proboscis above. Vault depressed to the level of the upper side of the arm- 

 bases, and provided with deep broad furrows or depressions radiating from 

 near the middle to the interradial spaces, composed of small, irregular, rather 

 tumid pieces. Opening in the summit of a short, rather narrow lateral pro- 

 boscis, which rises vertically, with its outer side nearly on a line with the verti- 

 cal side of the anal area. 



All the body plates are convex in the middle, from which point rather ob- 

 scure ridges radiate to each of their sides. The greater convexity and larger 

 size of the radial pieces impart a somewhat pentagonal outline to the body, as 

 seen from above or below. The surface is somewhat granular, and the col- 

 umn, which is composed near the base of alternately thicker and thinner 

 pieces, is round arfd pierced by a minute rounded cavity. 



Height of body, 033 inch ; breadth of do., 0-35 inch. 



Tliis neat little species is evidently closely allied to R. Barrisi, of Hall, from 

 which it differs in having its body plates merely convex and provided witli 

 radiating ridges, instead of being "ornamented by sharp, angular nodes and 

 spines :" also in having eight or nine interradial pieces to each area, instead 

 of only four to six. Another difference is to be obsei ved in the size of the third 

 radial pieces, which in R. Barrisi are "minute," while in our species they 

 are as large as the second radials. We only know the R. Barrisi from the 

 published description, but we have been assured by M. Wachsmuth, who com- 

 pared the form under consideration with authentic examples of that species, 

 that they are easily distinguished. 



[July, 



