60 PLATYCRINID^. — CYATHOCKINUS. 



for the rays, and iii-arched so as to partially cover in the vertex. This is particularly 

 conspicuous in C.yeometiicus, and appears to be very common in crinoids of this genus. 

 All the plates of the planus are smooth. 



Miller, at pages 80 and 87, represents the "scapulie" (lay -bearing plates) as "of a 

 form similar to those of Poleriocrinus." This is incorrect, as no plates can well differ 

 more widely. 



The Abdominal Plates. — In consequence of the inarching of the ray-bearing 

 plates, three or four plates are sufficient to cover in the vertex. These plates are 

 irregular in shape, and the central one is frequently the smallest of the group. 



The Mouth is lateral, prominent and protected by irregular-shaped calcareous plates, 

 which are also ananged round the base of the oral aperture. Two or three of these 

 plates, which are somewhat larger than the others, are built up on the non-ra}' -bearing 

 plate of the second series. 



It is strange that Miller should have seen a specimen with the mouth protruded, and 

 yet have omitted to ascertain its nature. In noticing the abdominal plates at page 87, 

 he observes, " In a specimen in the Ashmolean collection at Oxford this integument is 

 swollen out, and gives the specimen a singular appearance." But it seems he was not 

 aware that this protruberance was the true mouth. 



The Rays are single-jointed and bifurcate several times. The primary or main rays 

 are five, each composed of three single joints, above which Mr. Morgan's specimen, 

 represented in plate 7, figure 4, a, shews two other bifurcations ; but whether the rays 

 were further subdivided, none of the specimens we have seen enable us to decide. The 

 nvimber of digitations in this, and other crinoids may generally be relied on, though the 

 number of joints in each digit is not always constant, sometimes varying in different 

 specimens, or even in the same individual. 



The rays were no doubt tentaculated, although none of the specimens shew the 

 tentacula. The primary rays of all the known Cijathocrmi, amounted to five, but the 

 number of digitations probably varied in different species. 



The Column of the C. planus is circular, and the ossicula of its upper portion are 

 rounded inwards so as to make them less prominent at the points of articulation than 

 in their centres. The striae on the facets of the joints are chiefly marginal, the central 

 portions being smooth and often slightly depressed. The tubular canal running through 

 the column is circular. Miller has represented the uppei' portion as " quinquangularis;" 

 but as he has evidently mistaken the column of Poteriocrimis for that of the Cyathocrinus 

 planus, both in his figures and text, we consider him wholly in error on this occasion. 



The lower portion of the column figure 4, h, has a tuberculated appearance around the 

 prominent circumference of each joint, but this is probably produced l)y external causes. 



