380 PROCEEDINGS OF THE ACADEMY OF [1888. 



the overhans'ino; maro;ins of the his/her radials constitutiuo- the 

 lanceolate areas, partly the outermost interradial, and are limited on 

 either side by the inward extensions of the second and succeeding 

 radials. There are two sets of these lamellse to each interradius, 

 those of adjacent rays meeting laterally and entering the same 

 chamber where they are closely connected ; while those of the same 

 ray stand at an angle from each other, and are apparently disconnect- 

 ed except by a mere point. Each set is composed of five to seven 

 folded lamellae, with continuous walls forming loops at each end. 

 They stand upright, and seem to be attached at their lower ends to 

 the inner surface of the first radials, and those in the same ray come 

 together by their upper ends at a small angle under the small trian- 

 gular second radial, where it projects farthest inward. The upper 

 ends are further attached along the inner walls of the higher radials 

 and the outer interradials, underneath Avhich the two adjacent sets 

 meet by parallel plates and form a close connection. The arrange- 

 ment at the anal side is not clearly shown in any of the specimens. 

 In Enallocrinus we have not been able to discover anything of the 

 lamellae, but we had for examination but a solitary specimen show- 

 ing the interior of the calyx. There are seen, however, the same 

 chambered spaces in which they might rest, and we have little doubt 

 they existed in that genus also. Their position and structure in 

 Grotalocrinus rngosus are shown in our figures 11 and 1^. on Plate 

 XIX. 



From our description it must be clear that these laminated struct- 

 ures do not possess any of the characteristics of muscle-plates. Their 

 position in paired sets is interradial ; they are completely internal, 

 and have no visible connection with the arms, nor do they present 

 anv surface for the attachment of muscles or ligaments; but on the 

 contrary are very frail structures, having in some places little parti- 

 tions connecting the walls, and giving the whole a somewhat porous 

 appearance. On the other hand if we compare them with the hydro- 

 spires in the Blastoid genus Orophocrinus, one cannot help being 

 struck with the resemblance in form, position and arrangement. We 

 will not assert unqualifiedly that they are hydrospires, but we are 

 very confident that they are not muscle-plates, nor anything of that 

 nature, and if they are not of the same character as the similar 

 organs in Orophocrinus, which have been universally considered to 

 be hydrospires, then we must acknowledge ourselves completely at a 

 loss for anything in echinoderm morphology with which to compare 



