48 BULLETIN 115, UNITED STATES NATIONAL MUSEUM. 



three tyj^es in the Gurley collection, I have eight good specimens, 

 showing a range of from 15 to 20 arms, distributed as follows: Four 

 with 15 arms, one with 17, one with 18, and five with 20. The 

 characters otherwise are uniform in every essential particular. The 

 pictures of surface ornament in Miller and Gurlej^'s figures are not 

 always to be depended on, and those given of this form show more 

 difference among themselves than actually exists. 



Horizon and locality. — Hamilton (Sellersburg) limestone: Charles- 

 town, Indiana, and vicinity. 



DOLATOCRINUS COSTATUS Wood. 



Plate 12, figs. 1, 2, 3. 



Dolatocrlnus costatus Wood, Smithsonian Miscellaneous Collections, vol. 47, 

 1904, p. 70, pi. 16, figs, 6, 6a. 



A good representative of the amylus group, from the Traverse 

 beds of IVIichigan. In addition to the type figured by Miss Wood, I 

 have three other specimens, one larger and two smaller; all have 

 20 arms, except one, wliich has an extra arm in one ray. So the 

 number, toward which there was a strong tendency in the Louisville 

 area, is here well established at 4 to the ray. There is a difference, 

 not very clearly definable, in the style of sculptm'ing, due to the 

 strong wrinldes on. the plates of the cup, being in costatus less regu- 

 larly radiating: the tegmen plates are more distinctly outlined, and 

 the arms more nearly in a continuous ring. Pinnule openings are 

 very conspicuous — two and four between arms and four or six be- 

 tween the rays. The specimens range in size about as those of the 

 Louisville form — from 20 to 35 mm. high and 30 to 50 mm. wide. 



Horizon and locality. — Hamilton (Traverse) shales: Alpena, Mich- 

 igan. 



Form 6. ASTERIAS group. 



More or less rotund, with sides nearly vertical, truncate base and 

 small basal pit. 



DOLATOCRINUS ASTERIAS Wood. 



Plate 12, figs. 4-7. 



Dolatocrlnus asterias Wood, Smithsonian Miscellaneous Collections, vol. 47, 1904, 

 p. 71, pi. 16, figs. 1, Iff. 



A medium-sized species, but small specimens are found occasion- 

 ally. Calyx broadly basin shaped, more or less round above; sides 

 nearly vertical or slightly expanding upward, and base truncate, 

 with small, pentagonal-rimmed basal pit. Radiating striae strong 

 and coarse, those from the first interbrachials crossing the radials 

 and forming a conspicuous star surrounding the basal pit. Tegmen 

 low convex, not lobed, covered with rugose plates. Pinnule openings 

 conspicuous — two to each arm base and three or four in the interrays. 

 Arms 15, their openings directed obliquely upward. 



