KHODOCRINID^. 235 



Infrabasals five, small, pentagonal ; forming a flat, impressed pentagon 

 at the bottom of a concavity. Basals large, heptagonal, widely truncate 

 above. Radials angular at the bottom. Costals two. Distichals 2 X 10 in 

 the calyx ; the upper ones excavated to form the lower margins of the arm 

 openings, of which there are two to the ray, one to each main division. The 

 arms are in clusters, delicate, branching and biserial from the last axillary ; 

 they either stand erect and fold over the disk, or are pendent, their ventral 

 furrows exposed to view. Pinnules rather strong and closely packed to- 

 gether. Interradial areas large, composed of numerous plates ; those alter- 

 nating with the radials considerably larger and frequently nodose, the 

 interbrachials arranged in vertical rows. Anal interradius generally not 

 distinct in the cup. 



Ventral disk nearly flat, with five pit-like interradial depressions, of which 

 the posterior one is considerably the largest ; the bottom of the pits formed 

 by small polygonal pieces, surrounded by larger plates. In the European 

 species, in which the pits are less conspicuous or even wanting, the disk 

 plates differ but little in size. The outer margins of the disk are extended 

 outward, and form ten large tubular appendages, which are pendent, in some 

 species reaching down below the calyx. These appendages are formed either 

 by a single row of cylindrical joints, or by three rows of plates longitudinally 

 arranged, two of them ventrally disposed, the third dorsally ; but when two 

 of them are sutiirally connected, the consolidated part is composed of two 

 and six plates respectively. The tubes are all pierced to their full length 

 by a central canal, which, on entering the calyx, connects with the sub- 

 tegminal grooves at the inner floor of the disk. In the European species, 

 the ten appendages are free from their origin in the calyx, and those facing 

 the same interradius are separated from each other by interradial plates. In 

 the American forms, however, with the exception of G. spinigerus from the 

 Hamilton, and G. fiscelhis from the lower Burlington, the tubes meet in pairs 

 at midway between two rays, and are for some distance laterally connected 

 by a rigid suture ; but, although apparently forming a single appendage, 

 each one from the base up has its own canal, and the two canals of the same 

 set connect with different ambulacra. The arm or ambulacral openings are 

 located beneath the appendages ; they occupy the bottom of a small, funnel- 

 shaped pit, and are formed between the second distichals and the proximal 

 plates of the appendages. Anus subcentral, opening out directly through 

 the tegmen, and occupying the upper (inner) end of the posterior depression. 



