28 CALAMOGRINUS DIOMED^. 



remnant of a primordial pinnule in the fossil Antedon pinnatus, and that 

 this hook is separated from the joint by a suture. The proof of the ex- 

 istence of the so called primary pinnule can hardly be based upon the 

 indistinct figure he gives in Plate XXVI. Fig. 10^. The same may be 

 said of its discovery in Solanocrinus gracilis from Kelheim (Plate XXV. 

 Fio-. 2") ; and we cannot of course agree with him in also considering the 

 knobs of the axillaries of the genera which he figures in Plate XXIV. 

 Figs. 2'-2«, as the base of the first pinnule. The arm begins according 

 to him with this first pinnule. 



Side Plates and Covering Plates. 



The food groove of the ventral disk is protected laterally by a series of 

 plates arranged irregularly in a vertical plane. The base of these plates 

 either abuts directly against the inner rows of the perforated perisomatic 

 plates (Plate II. Fig. 3, Plate III. Fig. 2, Plate V. Figs. 1, 4, Rate VI, Figs. 

 1, 4, 5) ; or there are, especially near their junction with the oral plates 

 at about a third of the distance from the oral plates to the branch of the 

 food groove leading to the nearest pinnule, a number of irregularly shaped 

 protuberances or digitiform masses which separate these so called side plates 

 from the perforated plates of the perisome (Plate VI. Figs. 1, 2, Plate IX. 

 Fig. 1). 



On being boiled with pota.sh, the limestone plates forming these digiti- 

 form masses are found to be irregularly shaped polygonal, flattened, or 

 more or less cylindrical bodies (Plate X. Figs. 1-7). Some of them are 

 nearly smooth (Plate X. Fig. 1), others somewhat spiny (Plate X. Figs. 2-4), 

 and others again in the shape of spines (Plate X. Figs. 5-7). The reticu- 

 lation of the main body of these plates does not differ from that of other 

 plates ; it is more or less polygonal, but closer than that of the side plates 

 themselves (Plate X. Fig. 8). Towards the first branch of the food groove 

 of the disk the side plates become more prominently vertically arranged, 

 assuming the shape of lamellse with edges more or less lobed or spiny (Plate 

 V. Figs. 1, 4, Plate VI. Fig. 1), on the upper edge of which ride small 

 covering plates, which when pressed together close the food groove (Plate 

 V. Fig. 1, Plate VI. Figs. 1, 3-6). These lamellar side plates sometimes 

 extend well along the food groove of the arms as fiir as the third fork 

 (Plate VII. Fig. 13). The side and covering plates of the food groove of 



