ACTINOCEINID^. 581 



Type in the (Worthen) Illinois State collection, Sijringfield. 



Remarks. — In the specimens from New Mexico, the entire surface of the 

 calyx is covered with numerous irregular pustules, which are not represented 

 in specimens from the eastern localities. 



Steganoerinus araneolus Meek and Worthed. 

 Plate LXI. Figs. 2a, h. 



I860. Adinocrinus araneolus — M. and W. ; Proceed. Acad. Nat. Sci. Phila., p. 387. 



1866. Steganoerinus araneolus — lA. and W. ; Geol. Kep. Illinois, Vol. II., p. 198, Plate 15, K<»s. la, h. 



1881. Steganoerinus araneolus — W. and Sp. ; Rerision Palaeocr., Part II., p. 151. 



This form in its general structure agrees so closely with the preceding 

 one, that the question arises whether it is not a mere, variety of that species, 

 or perhaps its young stage. But the differences, such as they are, are so 

 constant among a large number of specimens, that it has been deemed safer 

 to treat it as a full species. It is not necessary, however, to give a repeti- 

 tion of the general structure, but it will suffice to point out the special 

 characters in which the two forms differ. 



Calyx from one half to one fourth the average size of 8. pentagoims, and 

 proportionally more depressed, its width to the top of the first costals equal 

 to once and a half its height. The plates of the dorsal cup more tumid, and 

 the ridges more prominent ; those of the tegmen more evenly nodose. The 

 basals are shorter, and almost invisible from a side view. It has but one row 

 of distichals instead of two, and only the plate at one side of the ray is arm- 

 bearmg. There are, as in the other species, two brachial trunks from each 

 ray, which stand out horizontally from the calyx, both arm-bearing, and each 

 one giving off from twelve to fifteen armlets. The palmars of both ray 

 divisions support an arm at the inner side of the ray, the post-palmars at the 

 outer, and so on from alternate sides. As a rule, each successive order 

 consists of a .single plate, but there are occasionally syzygies, at which the 

 arms are given ofC from the second plate, a fact which has never been 

 observed in the other species. The arms are short, and their joints are not 

 alternately spinous, but have serrated edges. In all other points this species 

 agrees with the preceding. 



Horizon and Locality. — Same as last. 

 . Type in the (Worthen) Illinois State collection at Springfield. 



