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ORDER AGELACRINOIDEA. 

 Family HEMICYSTIDiE. 



AESIOCYSTITES, n. gen. 

 [Ety. aisios, auspicious, coming at a good time; Kustis, bladder.] 



Body highly convex or hemispherical; free, not parasitic. We 

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

 tinued over the margin and part of the truncated side, and the 

 arms also 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 description. Plates 

 of the interbrachial areas non- imbricating and not coalescing with 

 the outer plates 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 con- 

 nects with the visceral cavity below. The ambulacral 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 HemicystUes, which is 

 a parasitic genus, composed of imbricating plates that coalesce 

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

 Type Aesiocystites prisons. 



