liemarks on the Goius Fterotocrinus. 5 



in nil the speciineus examined. The brachial pieces are arranged in 

 series of threes or fours on the third radials, and resemble them in 

 form, except that the ratio of the height to the width is greater. 



The Arms. 

 These are without Ijifurcations or divisions, composed of a double 

 series of interlocking plates, forty to sixty in each series, gradually 

 tapering to thew" extremities, and bearing two rows of stout, short, five 

 or six jointed pinnulae. The arm-plates are deeply excavated centrall}' 

 on the ventral surface by the ambulacra! grooves, from which radii are 

 continued into the pinnulpe. The arms are long enough to fold over 

 the top into the space at the base of the interbrachial rays. 



The Vault. 



This is p3'raraidal an<l pentagonal in form, four of the sides being 

 equal, while the fifth or az3^gos side is about one fourth larger than the 

 others. It is composed of series ot heavy plates, articulated in such a 

 manner that the five angles are excavated for the reception of the inner 

 ends of the interbrachial rays, which do not penetrate the vault, but 

 are articulated to it at the five angles, and are held in place by the 

 lower outer piece of the angle, which bears on its inferior, outer side, 

 a hook-like process, locking into the lower inner edge of the ray. The 

 sides of the vault are made up of series of pieces, diftering much in 

 shape and size. 



The lower series consists of three pieces on each side of the vault 

 except the az3^gos side which has four. These pieces, and those at the 

 lower ends of the angles, comprise the base of the vault." They are 

 folded inwardly, and in transverse section are shown to articulate 

 below with the radials, as the inner side of the first radials is reflected 

 upward to meet them. The sutures of these plates are perforated by 

 the pores communicating with the arm furrows. These pores are 

 slightly funnel-shaped, directed upward exteriorl}^, and excavate the 

 second and third radials interiorly', opening into the pelvic cavit}-; So 

 far as can be determined by numerous cut specimens, there is no 

 skeletal division of the cavity inside either of the vault or pelvis, 

 which, on such a supposition, was a shallow, saucer-shaped cup, ter- 

 minated upvvard by a pentagonal pyramid. There is no dome roofing 

 the pelvic cavity, and separating it from that of the vault. The latter, 

 above the basal series of plates already described, is formed of hexa- 

 gonal and pentagonal pieces, of different proportions in the various 

 species, and is in some cases terminated by a number of small plates, 

 the precise arrangement of Avhich can not be determined. The top of 



