THE FOSSIL CRICOID GENUS DOLATOCRINUS AND ITS ALLIES. 49 



The basal star is a most striking and constant character, by which 

 the species is readily recognized from the base alone. I have 25 

 specimens, in all of which it is perfectly distinct. Among 13 speci- 

 mens in which the arm openings are observable, 10 have 15 arms, 

 and one each 13, 14, and 16. In size the specimens range from 18 

 to 25 mm. high and 25 to 32 mm. wide, with a few somewhat larger 

 or smaller. The average height to width is about 1 : 1.35, the smaller 

 specimens being relatively higher and the larger ones lower. 



Horizon and locality. — Hamilton group: Alpena and Partridge 

 Point, Michigan. 



DOLATOCRINUS INCISUS. new species. 



Plate 12, figs. 8-13. 



Similar to asterias, with which it is associated, but with more 

 broadly concave base, and without the strongly modeled basal star, 

 although a stellate arrangement of triangles is apparent in some speci- 

 mens. Kadiating striae sharply incised, wrinkled, forming triangu- 

 lar figures, either single or enclosing others. Tegmen broadly lobed. 

 Pinnule openings obscure, probably two to each arm base. Arms 20. 



The type of sculpturing is similar to that of Stereocrinus triangula- 

 tus, and unlike that of other Michigan forms of this genus. I have 

 seven specimens of this form, ranging in size from 10 to 23 mm. high 

 and 16 to 36 mm. wide; six of them show all the arm openings, 

 which are 20 without exception. 



Two specimens are figured, to show the extremes of fine and coarse 

 sculpturing of the same type.- 



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

 gan. 



Form 6. VENUSTUS group. 



Calyx small to medium size, bowl-shaped, hemispheroidal, not 

 constricted below the arms; sides curving evenly to arms from nar- 

 row base, not concave. Tegmen low. Pinnule openings incon- 

 spicuous — 2, or perhaps only 1, to each arm base. Arms, 15 to 20. 



This general description includes a group of six species by Miller 

 and Gurley and one by Rowley, among which I have attempted to 

 separate three definable forms. All are typically small species, 

 having about the same general proportions, and ranging from 8 to 

 20 mm. high and 12 to 28 mm. wide, the average height to width 

 being 1:1.5. I have 22 specimens besides the tyi>es of Miller and 

 Gurley, minus that of exornatus, which with two other of their types 

 was lost before the Gurley collection was received by the University 

 of Chicago, and for which we must rety upon the figures and de- 

 scriptions. The arms in these 28 specimens vary from 12 to 20, dis- 

 tributed as follows: with 12 arms, 1; with 13 arms, 2; with 15 

 arms, 3; with 16 arms, 6; with 17 arms, 8; with 18 arms, 1; with 

 19 arms, 4; with 20 arms, 3. 



