CALYPTOCRINID^. 333 



than the second. The first palmars support the arms ; they are short, trun- 

 cated at the upper face, and are provided with small muscle plates and 

 fossae. First interbrachials generally the largest plates of the dorsal cup, 

 more than twice as large as the two above. The two latter are of about the 

 same form and size, and are in contact laterally to their full length. They 

 rise some distance beyond the top of the palmars in square or tapering trun- 

 cate projections, and jointly form a support for the interradial partitions. 

 The interdistichals rest either within notches formed by the distichals, or 

 upon the truncate upper face of the second costals. They resemble in form 

 the combined upper interbrachials, rise like these to the height of the third 

 arm plates, and support in a similar manner to the interbrachials a partition 

 wall upon their truncate upper fxces. The projections between the arm 

 sockets give to the specimens a very marked aspect, and serve as a reliable 

 guide for generic identification in case the ventral structures of the calyx 

 are not preserved ; in that condition they look like cogs of a wheel. 



The tegmen, or part above the dorsal cup, consists of four rings of plates 

 of peculiar structure. The lower ring is composed of ^Ye elongate inter- 

 radial pieces which rest upon the projecting upper faces of the interbrachials, 

 and five plates of similar form and size supported by the interdistichals. 

 The middle portions of the ten plates extend outward and upward in. form of 

 knife-like winged processes, of which the upper end rises to near the fourth 

 row of plates, overlapping the plates of the second and third rows, to the 

 outer faces of which they are attached by suture. Interposed between these 

 plates are ten small trigonal pieces, arranged in such a manner that a plate 

 supported by an interbrachial, and one supported by an interdistichal, always 

 meet laterally over the top of one of the triangular pieces. The latter plates, 

 which are somewhat thickened at their median lines, form a sort of subpar- 

 titions between the arms of the various pairs, without being visible when the 

 arms are intact. Their edges at both sides, and also those of the larger 

 plates, are pierced by the ambulacral or arm openings, which are well 

 defined in this genus, and enter the calyx between the two plates. The 

 second and third rings, which form the tubular prolongation of the calyx, 

 are composed of four plates each ; the fourth ring consists of ten pieces, 

 which meet around the summit. The plates of the second ring slope 

 upwards; two of them are wider, and alternate with the other two; the 

 two narrower plates are longer, and angular at the top, the others truncate. 

 United they form an inverted funnel, the margin surrounded by ten protu- 



