CALAMOCRINUS DIOMEIXE. 33 



The second set is made up of smaller plates extending from the lateral 

 plates of the food groove round the peristome towards the imperforated 

 plates. These smaller plates are somewhat thinner, perforated, and arranged 

 in from four to six irregular rows. Figure 1 of Plate VI. gives a general 

 view of the arrangement of the perisomic plates seen facing the mouth. 



The small plates in the anal interradium are not perforated (Plate II. 

 Figs. 2, 4, Plate III. Fig. 5, Plate V. Figs. 2, 3, Plate VI. Fig. 1). In Plate 

 II. Figs. 1, 3, Plate III. Pigs. 1, 2, Plate V. Figs. 1, 4, and Plate VI. Fig. 5, 

 the relation of the perforate to the imperforate j^lates is shown for different 

 interradial spaces.*. 



There is apparently little regularity in the arrangement and size of this 

 perisomic plating. Even the lower rows of larger imperforate plates ad- 

 joining the upper faces of the radials differ not only in different specimens, 

 but in different interradii of the same specimen. Compare Plate II. Figs. 

 1, 3, 5-13, Plate III. Figs. 1, 2, and Plate V. Fig. 1. 



The lower rows of large imperforate plates abutting upon the radials 

 are in no wise to be distinguished from similar plates figured by D'Orbigny 

 and de Loriol for Apiocrinus and Millericrinus. They unite the adjacent 

 arms into a rigid calyx ; and an examination of the figures of some of 

 these imperforate plates (Plate IV. Figs. 9-14) shows that they are fully as 

 solid and compact as the so called calyx interradials of the Apiocrinidge 

 proper. 



It is true that they occupy in some cases among the fossil Apiocrinidre 

 a somewhat different interradial position from that which they hold in 

 Calamocrinus, in the former cases filling only a comparatively small space 

 left between adjoining arm.s. But their mode of junction, either with the 

 arm joints, or with the joints of the pinnules, or with the upper faces of 

 the radials, is such as to make a complete and firmly united mail of plates, 

 and to form with the calyx a large rigid cup, expanding in width gradually 

 from the dorsal face of the basals and the lower parts of the arms nearly 

 to the first axillary. f 



The wing-like projections from the sides of the arm joints uniting them 



* Peri-ier states (Organisation et Developpement de la Comatule de la Mediterrane'e, Nouv. Arch, 

 dii Museum, IX. 26 Serie, 1866) that the water pores are wanting in the anal interambulacral area of 

 Actinometra (p 101), while they are found over the whole disk of Pentacrinus and Autedon. 



In Hyocrinus the anambulacral plates are perforated by water pores, but not in the anal interradium. 



t The ventral disk and arms both in Antedon and Actinometra are devoid of continuous plating 

 (Carpenter, Chall. Rep.), yet it may be strongly developed between the lower division of the rays 

 extending up to the level of the third axillary. 



6 



