152 NEW YORK STATE MUSEUM 



Found in the Rochester shale at Lockport (Hall). Isolated frag- ■ 

 ments of plates have been obtained from the weathered lower 

 Rochester shale in the Niagara gorge. 



Class CRINOIDEA Miller 



The crinoids, or sea lilies, are marine invertebrates, represented 

 in the modern seas by a number of genera and species which range 

 from shallow water to a maximum depth of about 3000 fathoms. 

 They are gregarious in habit, and usually of very local distribution. 

 A typical crinoid consists of a dorsal cup or calyx, placed on a stalk 

 or stem, by means of which it is attached, and bears a fringe of arms, 

 variously divided and furnished with jointed appendages, or pin- 

 nules. The calyx is composed of a number of plates, which have a 

 definite arrangement, in horizontally disposed series (fig. 50). The 

 lowest of these are the basals, though in many forms an additional 

 series, the infrabasals, may underlie and alternate with the basals. 

 Next above the basals, and alternating with them in position, are 

 the radials, five in number, so called because they are in line with 

 the rays or arms. Referring the position of the inferior plates to 

 that of the radials, we find that the basals are always situated inter- 

 radially, while the infrabasal are situated radially. Above the 

 radials lie the brachials. These vary greatly in number and kind, 

 sometimes articulating directly with the radials, in which case all 

 the brachials are free, and sometimes having their lower series fixed 

 and immovable, thus forming a part of the calyx. The brachials 

 lying directly on the radials are the costals; of these there may be 

 one or more series, when they are distinguished from below as 

 primary (cost.^), secondary (cost.^), etc. The uppermost costal of 

 each ray is commonly axillary, i. e. pentagonal in outline, with two 

 upper joint edges inclined from each other. On these rest the 

 distichals, of which there are 10 in each series. Secondary distichals 

 (dist.^) may rest on the primary ones (dist.^), and may in turn sup- 

 port the palmars, of which there would be 20 in a normal series. 

 Above these, on farther division, are the post-palmars, which are 

 often very numerous. Two types of arms can be distinguished, 

 those composed throughout of one series of plates (uniserial), and 

 those made up of a double series (biserial), the plates of the latter 

 usually interlocking to a greater or less extent. The latter are the 

 more specialized, always beginning uniserially. 



Between the radials are often found additional plates, the inter- 

 radials, which may vary in number. 



Between the distichals of one ray may occur the inter distichals,. 

 which are situated radially. Between the distichals of adjacent rays 

 may occur the interbrachials, and these will be situated inter radially.. 



