MELOCRINID^. 311 



of the interradial plates is invariably the same at all sides, but at the anal 

 side the ventral disk has a few additional pieces, and the plates pierced by 

 the slits are shorter. The disk contains large orals, pushed anteriorly by 

 the stout, almost central anal tube, and it has well defined radial dome 

 plates of a first and second order. Ambulacra subtegminal. Column large, 

 round ; the sides covered in some of the species by large angular processes 

 or ribs ; axial canal very large and pentalobate. 



Distribution. — Kestricted to the Upper Helderberg and Hamilton groups 

 of America. 



Ti/2:)e of the genus. — Dolatocrinus lacus Lyon. 



Remarks. — The complete anchylosis of the basals, the large size of the 

 first interbrachial and its being followed by a single plate, the large anal 

 tube, and the slit-like openings at the sides of the arms, together with the 

 perfect symmetry of the dorsal cup, form excellent characters of this genus. 



Lyon described the base as composed of Wyq pieces, while Hall mentions 

 three basals, but the fact is that the sutures are not visible externally in the 

 specimens. Mr. Victor Lyon, however, sent us a specimen in which the 

 presence of three plates is indicated at the inner floor, while no suture 

 lines appear exteriorly. 



The slit-like openings have not been noticed before. We regard them as 

 analogous to the respiratory pores of Batocrinus, from which, however, they 

 differ in number, form and arrangement. 



Hall, in 1862, described several species of the type of Dolatocrinus under 

 Cacabocrinus, a catalogue name of Troost, and among them Cacahocrinus 

 Troosti and C. lamellosus, of which we have been unable to get authentic 

 specimens. The descriptions are too general for specific identification. 



Dolatocrinus lacus Lyon. 

 Plate XXVI. Figs. 6a-c. 



1857. Lyon; Geol. Eep. Kentucky, Yol. III., p. 482, Plate 4, Pigs. 3, 2a-c. 

 1881. W. and Sp. ; Revision Palfeocr., Part II., p. 126. 



Calyx depressed hemispheric, flattened below, somewhat tumid around 

 the summit. Dorsal cup more than once and a half as wide as high ; the 

 basals and the lower half of the radials deeply incurved, and formed into an 

 inverted funnel-shaped concavity, which is wider than the column, the latter 

 touching only the bottom part. The upper half of the radials, and nearly 



