INVERTEBRATES. 187 



other very short, wide pieces, upon the last of which the first 

 divisions of the arms rest. 



Two of the anal pieces are visible in our specimen, resting 

 upon the largest subradial, and apparently each supporting, or 

 connecting with, one of the inferior lateral edges of a first radial 

 on each side. It is of moderate size, pentagonal, and supports 

 a smaller piece of unknown form, on its upper truncated side, 

 while its left superior sloping edge connects with another small 

 piece, apparently of a pentagonal form, resting upon a short 

 truncated upper side of one of the subradials. 



The arms are nearly flat, or but slightly rounded on the 

 outer side, and bifurcate again after the first division on the 

 second radial pieces (in the lateral and posterior rays), on the 

 eighth, tenth and eleventh pieces ; one of each of these divi- 

 sions subdivides again on the twelfth or fourteenth piece, be- 

 yond which they all appear to be simple. The entire length 

 of our specimen, to the extremity of the arms, is about 1.50 

 inches. Height of body, to summit of second radials, 0.20; 

 breadth of do., at the top of second radial pieces, near 0.40 

 inch. 



Fig. 4. 



^~"~ \ This species is related to Zeacr-inus ramosus, Hall, 



\^y (Iowa Keport, p. 549, pi. ix, fig. 3,) but differs in 

 {S//^^r^ having its arms more flattened, and broader on the 

 outer side. They also bifurcate less frequently, and 

 the number of pieces between the bifurcations is con- 

 / ^ /"v siderably greater. Its second radials are likewise pro- 



portionally shorter, as are all the arm pieces. Again, 

 all the divisions of its arms are given off much less 

 obliquely than in Z. ramosus. The specific name was 

 given in honor of Prof. G. Troost, deceased, former 

 State Geologist of Tennessee, and the founder of the 



Zcacrinus Troostanus. 

 Somewhat enlarged. genus 



If Zeacrinus should be hereafter found to be synonymous with Graphiocri- 

 nus, as has been suggested, the name of this species would of course become 

 GrapMocrinus Troostanus. 



Locality and position: Burlington, Iowa, Burlington Limestone, of Lower 

 Carboniferous series. 



C0B» 



