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ORDER AGELACRINOIDEA. 

 Family HEMICYSTID.E. 



AE8I0CYSTITES, n. geu. 



[Eiy. (lisios, auspicious, coming at a good time; Kiislis, bladder.] 



Body liigbly convex or hemispherical; free, uot parasitic. AVe 

 say free, because the plates preserved in our specimens are cou- 

 tiuued over tlie margin and part of the truncated side, and the 

 arms ulso curve over the margin before they terminate. The 

 truncated side is depressed in our specimens and is not preserved 

 so as to offer an opportunity for an intelligent descri2:)tion. Plates 

 of the interbrachial areas non- imbricating and not coalescing with 

 the outer phites of the arms. Arms five, very large, highly con- 

 vex, radiating from the center and curving over the margin be- 

 fore they terminate. They are composed externally of a double 

 series of alternating and interlocking plates; when these plates 

 are removed deep gutters are disclosed, which are angular at the 

 bottom, and unite in an elliptical hole at the center, which cou- 

 nects with the Tisceral cavity below. The ambulaeral furrows and 

 central orifice are completely covered with the alternating and in- 

 terlocking arm plates. One interbrachial area is larger than the 

 others and the anal or ovarian pyramid is situated in it, eccen- 

 trically, approaching the margin. 



This genus is readily distinguished from Hciiiici/sfiles, which is 

 a parasitic genus, composed of imbricating plates that coalesce 

 with the arms, which are limited by a marginal rim of plates. 

 Type Aesioci/stites 2JJ'>scns. 



