THAUMATOMETRA NUTRIX. 



57 



In the next stage represented (plate xxvm, figure 3) the radials have 

 grown somewhat and assumed a triangular shape; the costal has appeared 

 as a branching spicule. The anal plate lies wholly outside the radial mid- 

 line; it has hardly any influence upon the shape of the adjoining radial 

 plate in this stage. The stalk-joints can not be discerned in the upper 

 part of the stalk; the lower ones are assuming their final shape. 



In the following stage (plate xxvm, figure 4) the arms have begun to 

 form; the radials are joining, thus separating the basals from the orals. The 

 anal plate is still small, but the radial to the right of it is now considerably in- 

 fluenced by it (text-figure 8) ; a naked space, 

 only partly occupied by the anal plate, 

 separates it from the adjoining radial plate 

 to the left. Also the adjoining oral plate has 

 undergone some absorption. The costals are 

 long and narrow, the original spicule still 

 being discernible in the middle. The axil- 

 laries are somewhat shorter ; along their 

 outer edges the arm-joints have begun to 

 appear in the typical shape of a spicule 

 lying transversely and sending out prolonga- 

 tions proximally and distally. The upper 

 stalk-joints are still indistinctly separated 

 from one another. A slightly more advanced 

 stage is that figured in plate xxvm, figure 

 5. The arms have grown considerably, about 

 6 joints having developed. The axillary has 

 assumed its typical shape with two oblique 

 outer edges. The primary spicule is still dis- 

 tinct, both in the axillary and the costal. The stalk-joints are now assuming 

 their final shape also in the upper part of the stalk. There are still only 11 

 joints, the same number that was found in the youngest specimen. 



The last stage found is that represented in plate xxvm, figure 6. Unfor- 

 tunately not one of these specimens is in good condition, the arms being 

 broken off more or less completely. The first pinnule has appeared ; it is on 

 the twelfth arm-joint. The disk has already grown fairly large, the oral 

 plates being now widely separated from the calyx plates. They are of some- 

 what larger size than usual. The anal cone has been formed and the anal 

 plate remains distinct close to the adjoining oral plate. The cirri are very 

 far advanced in development ; those of the first whorl are fully formed, with 

 a conspicuous terminal claw and opposing spine; they consist of 12 joints 

 of about equal length. As usual, the first 5 cirri are radial in position. The 

 second whorl is about to develop, alternating with those of the first whorl. 

 The stalk-joints have now attained their final shape. They are rather short, 



FIG. 8. Pentacrinoid of Thaumatometra 



nulrix, same stage as that represented in 

 plate xxvm , figure 4, showing the relations 

 of the anal plate. X100. 



