THE FOSSIL CRINOID GENUS DOLATOCRINUS AND ITS ALLIES. 35 



wise to enable them to give a recognizable definition from which 

 the species can be identified beyond any question. With about 50 

 specimens in my own collection for comparison, many of them very 

 well preserved, the essential characters are clearly evident, as the 

 new figures show. 



As in the case of D. grandis, this is typically a large-sized species, 

 33 of the specimens being from 40 to 55 mm. in width, and 8 from 

 30 mm. down to a minimum of 15 mm. wide, the remainder being 

 intermediate; the average height to width of the calyx is about 1: 

 1.65, and the height of the dorsal cup is usually more than half 

 that of the calyx. Below the arm openings the calyx is depressed 

 hemispheroidal, shallowly concave below, with column facet abruptly 

 sunk, involvmg only the basals. The first interbrachial is a very 

 large plate, 11-sided from the abuttmg of IIIBr due to the second 

 bifurcation in the ray, giving 4 arms to the ray contrasted with the 2 

 in D. grandis; this plate is truncate above, supportmg one large 

 median second interbrachial, as usual in the genus, with the sole 

 exception of D. grandis. 



The surface ornament in general consists of fine radiating lines, 

 producing combinations which take the form of included triangles, 

 and sometimes crossed by others, causing a pitted appearance. The 

 one conspicuous feature of the sculpture is a strong, keel-like ridge 

 along the radial series, which however is always confined to the radi- 

 als and primibrachs. This keeled protuberance varies in shape 

 from a fairly strong rounded ridge to a very high, knifelike edge; 

 but it never passes along the ray beyond the primibrachs. 



The tegmen is moderately convex, sometimes more or less conical, 

 broadly but not deeply lobed, and surmounted with strong spines 

 above the ambulacral series and around the base of the tube. Pin- 

 nule openings four to the interray, the outer pair often broken away ; 

 and two, sometunes four, in the spaces within the ray; not so promi- 

 nent as in D. grandis. 



With such a large number of specimens in hand it is interesting 

 to see how true to type they run. Out of 21 specimens having the 

 tegmen intact, all except 3 have strong spines, and in these, although 

 rather weak, the projections are nevertheless pointed spines. Of the 

 20 specimens in which the arms can be counted, the only departure 

 from the normal 20 arms is seen in two specimens which lack an arm 

 in two rays and in one ray, respectively. 



Rowley's D. curriei is merely a typical specimen with the surface 

 ornament preserved, which was lacking in the type. 



Horizon and locality .—Onond&ga (Jeffersonville) limestone: Louis- 

 ville, Kentucky, and vicinity. 



