JI3. CONTRIBUTION TO 



above two smaller platen which rest below two still smaller pieces. Above 

 these and between the arm lobes are four or five elongate small plates. 



The plates of the ventral disk are slightly convex, and the anal opening or 

 base of anal tube, is nearly central and rather strong. The ventral portion of 

 the fossil is badly weathered, and surface features may be obliterated. 



There are ten large arm bases (two to the group). Lobes not distinct. 

 From six to seven slits pierce the plates b(?tween the arm groups, just at the- 

 periphery, and from four to five between the arm bases of the same group. 



The dorsal cup of the specimen is beautifully preserved and, unlike 

 either I). iii(H'x/n or I). crcdratK.^ has no keeled radial ridge, the entire- 

 surface being ornamented by numerous, low sharp lines radiating from the 

 centers of all the plates and with short, connecting ridges, giving a delicate 

 pitted or reticulate appearance to the test, with but the merest indication of a 

 radial ridge. The dorsal plates are wholly without central nodes. 



The great height of the ventral disk of this form and the non-keeled char- 

 acter of the radial rays separate it from J), excavattis, which Wachsmuth and 

 Springer describe as strongly keeled and with a depressed ventral side. 



The handsome specimen figured is from the middle Devonian, Thompson's 

 Bend, on Silver Creek, Clark county, Indiana, and belongs to the collection of 

 Mr. G. K. Greene. 



I) O L A T O C K I N U S P E R N O I) O S U S, N. Sp. (Rowley. ) 



Platk 85. FktS. 4, 5, 6. 



The dorsal cup of this fine crinoid is concave below the first interradiali 

 l)lates, broadly but much less deeply than in the preceding species. The out- 

 line of the ])entagonal basal disk is seen at the bottom of the broad, shallow 

 concavity. Tlie first radials are about as wide as long and convex, with low,, 

 sharp ridges radiating fron) the center to the centers of adjoining plates. The- 

 second and third radials are much wider than long and strongl}- convex or no- 

 dose. As in the first radials, sharp radiating lines pass to adjacent plates. 

 The iirst jilates of the second series of radials are each axillary and (juite as 

 large as the radial i)lates below them, strongly convex and giving rise to sharij> 

 radiating ridges. Each plate of the third series supports above two plates,, 

 making three times four ])lates to the third radial series. 



The first interradial i)late is the largest plate in the l)ody, as wide as lon<^, 

 strongly tumid with radiating ridges from the center to the centers of neijjfh- 

 boring plates. Above the first interradial is a large, tumid second interradial 

 above which is a smaller plate supjiorting above two still smaller plates. All of 

 the dorsal j)latesare strongly tumid and with sharp radiating lines from center to- 

 center of adjoining plates. 



