MELOCRINID^. 293 



sutiirGj and form together rigid tubular appendages, which pass out from the 

 calyx upwards. In some cases the connection of the appendages is inter- 

 rupted for short distances, but^ so far as known, all of them come together, 

 and are united toward the upper part. From these appendages throughout 

 their full length, at certain intervals, and from opposite plates (not alter- 

 nately) are given off w^ell defined biserial arms, bearing pinnules on alternate 

 sides. A slight departure in the construction of the main trunks occurs among 

 species in which the proximal arms are given off already from the first 

 axillaries, /. ^., from the costals. In these species the trunks at the dorsal 

 surface are composed of but a single series of plates, and the pinnule-bearing 

 arms are arranged alternately as in Steganocririus sculptus. The ventral sur- 

 faces of the appendages are roofed over in all cases by rigid covering plates. 



Interbrachials numerous ; the first placed upon the sloping upper faces 

 of the radials, followed by two plates in the second row at the four regular 

 sides, three plates at the anal side, and a greater or less number of irregular 

 plates above, which meet with the interambulacral plates. Ventral disk 

 highly elevated or scarcely convex ; the orals in some species largely de- 

 veloped, in others indeterminable. Anus excentric and generally — perhaps 

 always — extended into a small tube. 



Column round, composed of alternate long and short joints ; axial canal 

 small. 



Distribution. — Melocriiius ranges from the Upper Silurian to near the 

 close of the Devonian, and is well represented both in America and Europe. 



Remarhs. — The genus Melocrinus holds the same relation to Mariacrinns 

 that Steganocrinus does to Actmocmus, and Eiidadocrinus to Platycrinus. In 

 all these types the construction of the calyx remains relatively almost un- 

 changed, while a remarkable modification occurs in the brachial appendages, 

 which are extended into tubular rays with an indefinite number of semi-free 

 brachials, giving off arms. 



Several attempts have been made to subdivide Melocrinus vnio two or 

 three genera. Roemer, in 1855, proposed the name Castanocrinus for 

 species with a central or subcentral anal opening, retaining Melocrinus, with 

 M. hieroglypMcus Goldfuss as type, for species with a lateral opening. Our 

 examination of the various species leads us to doubt whether such a division 

 can be practically upheld. We agree with Schultze ^ that the anus is never 

 central in this genus, nor in any case actually lateral, but its position is 



* Mouogr. Eifl. Kalkes, p. 63. 



