1879.] NATURAL SCIENCES OP PHILADELPHIA. 281 



course would remove Iihopalocrinus from the Ichthyocrinidse, 

 and bring it in close relation with such genera as Symbathocrinus 

 and Pisocrinus, with which it agrees in its arm structure and in 

 the narrow proboscis, which probablv extended in those genera to 

 the extremities of the arms. 



We propose the following generic diagnosis: General form of 

 bod}', including arms, subelavate, with bilateral S3nnmetry ; plates 

 heavy. Underbasals three, scarcely visible beyond the column. 

 Basals five, four of them equal, regular^ pentangular, the fifth 

 much higher, becoming narrower toward the top, truncated above 

 for the accommodation of the proboscis. Radials placed in a 

 direct line with the arms ; one ring only constituting a part of the 

 solid body, all succeeding ones be'ng more or less movable. First 

 radial large, heavy, the articulating face occupying almost the 

 entire width of the plate, circular, facing slightly outward, and 

 perforated with an opening which communicates with the inte- 

 rior body and with a passage toward the dorsal side of the arras. 

 Second radials, or first brachial plates, wide but short, evidently 

 movable, probably connected interradially (between the rays) by 

 small polygonal plates. Succeeding plates all of the same width 

 and form as those of the preceding ring; their height, however, 

 three or four times greater. Arms five, simple throughout, and 

 closely resembling those of Symbathocrinus ; length unknown, of 

 almost uniform size up to the sixth plate. Ambulacral furrow 

 covered by two rows of plates roofed together, with the median 

 line elevated. Anal area supporting a lateral proboscis similar 

 to that of Onychocriniis, but heavier, and probably extending up 

 to the top of the arms, as in Symbathocrinus. Interradial spaces 

 apparently filled b} r very small, uneven polygonal plates up to the 

 second brachial. Column large, almost cylindrical, and composed 

 of larger and smaller joints near the body. 



The only known species is 



*1866. Rhopalocrinus gracilis Schultze. (Taxocr. gracilis Schultze, not Taxocr. 

 gracilis Meek and Worth.) Monogr. Echinod. Eifl. Kalkes, p. 39, pi. 4, 

 figs 3, 3 a. Devonian. Eifel, Germ. 



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