260 PROCEEDINGS OF THE ACADEMY OF [1881. 



being an angular process in the middle. Second radials^ very 

 minute, often not visible externall}^ and resting from within 

 against the median angular process within the articulating depres- 

 sion of the large radial. Their inner face is much larger, trian- 

 gular in form, with concave sides. The arrangement is such that 

 these sides, together with the outer portions of the articulating 

 scar of the first plates, form two semicircular sockets, supporting 

 each a small pentagonal bifurcating secondary radial, which here, 

 as in Pterotocrinus and Ilan^upiocrinus, constitutes a part of the 

 bod}-, and in turn supports two arms, or twenty arms in all. 

 Form of the arms unknown. 



Vault generally of equal height with the calyx, decidedly lobed 

 when viewed from above ; composed of numerous small pieces, 

 some of them spiniferous ; toward the posterior side obliquely 

 flattened, with a lateral anal aperture towards the upper end. 

 Radial area elevated, and extending outward ; interradial portions 

 depressed, posterior side much wider. Central vault piece large, 

 nodose or spiniferous. The four large proximal plates occupy in 

 four of the interradial spaces the upper portion of the depression, 

 while the two smaller ones rest partly against the radial portions 

 of the dome, with several small anal plates and the anal aperture 

 between them. Interradial vault pieces three, rather large, and 

 much higher than wide. The first radial vault piece is spiniferous 

 in most species, the succeeding plates small and nodose, arranged 

 longitudinally in rows, forming together regular arches over the 

 ambulacral passages within the body. There is a large elongate 

 brachial piece between the two divisions of each ray, which at its 

 lower end connects with the upper point of the second radial, 

 thus giving origin to two arm openings in each ray. The anal 

 area has three large pieces in the first series, which rest upon the 

 anal plate of the calyx, the median one has form and size of the 

 interradial plates, the two others are smaller. In the second 

 series there are two plates, followed by a number of minute pieces 

 surrounding the anal aperture, which is protuberant. 



Column probably cylindrical and small, with a minute central 

 canal. 



Talarocrinus differs from Dichocrinus in the greater promi- 

 nence of the plates in the calyx ; its higher vault ; in having the 



' Shumard described Dichoer. cornigerus with a single radial, but the 

 second is present in the species though hidden from view exteriorly. 



