30 CALAMOCRINUS DIOMED.E. 



The reticulation of the side plates is at first quite regular, made up of 

 circular or elliptical meshes (Plate XII. Figs. 3, 6), the walls separating the 

 meshes varying greatly in width and thickness. As the side plates increase 

 in size and thickness, the regular reticulation becomes more or less obscured 

 by the formation of a second, or even a third or fourth, floor of calcareous 

 meshwork. The secondary meshwork thus formed is very irregular in out- 

 line, the walls separating adjoining cells x-unning in all directions, becomino- 

 frequently anchylosed with vertical or horizontal rods uniting toarether a 

 series of cells on different planes. Figure 5 of Plate XII. shows one of the 

 side plates in which the secondary reticulation has been formed principally 

 at the upper end, the remaining part of the side plate still showing the 

 original reticulation. In Figures 2, 4, Plate XII., the secondary reticulation 

 has obscured the primary reticulation of nearly the whole of the side plates; 

 and in Figure 1 there is no trace of it to be seen through the soldering 

 of the limestone rods of the different planes of the meshwork. 



In Plate XI. Fig. 1, there Is a tendency to anchylosis of the adjoining 

 cells, and the first appearance on one side of the side plate of the secondary 

 reticulation to form lateral spines, such as have been figured in Plate VII. 

 Fig. 1. An enlarged view of this secondary reticulation is shown in Plate 

 XI. Fig. 5, forming the ba.se of a lateral spine of a side plate, and Figures 

 6, 7, of Plate XI. show two of the lateral spines of a side plate in different 

 stages of development. The reticulation of the side plates of Plate VIII. 

 Fig. 1, is a combination of the conditions of the secondarj' reticulation found 

 in Plate XI. Fig. 1, and Plate XII. Fig. 5. 



The side and covering plates of the groove of the pinnules do not differ 

 in their arrangement from that of the arms. Their shape and structure 

 presents about as great variation in the pinnules found near the base of 

 the arms and those near the middle or extremity of the arms and forks 

 as do the corresponding parts of the arms. We find the same lateral 

 processes of the side and covering plates in pinnules close to the disk (Plate 

 VIII. Figs. 8, 9) which we find in the covering and side plates of the food 

 groove near the base of the arm. As we pass to pinnules nearer the ex- 

 tremity of the arm, the covering and side plates become more simple (Plate 

 VIII. Fig. 10). The original elliptical reticulation of the side plates is grad- 

 ually obscured in the side plates of the groove of the pinnules, as it is 

 in the side plates of the arm food groove (Plate XI. fig. 10). 



The reticulation of the irregularly shaped covering plates of the food 



