CALAM0CRIN1 S DIOM1 D I 17 



the base, in which the rings have become absolutely discoidal, and thai 

 in which the rings arc ribbed, we find a transition in some cases in which 

 the ribs become very indistinct, and are merely marked by an angular 

 outer outline (Plate X \ II Figs. 12, L3, II). before they become rings with 

 the convex outer outline of the lower pan of the stein. The specimen in 

 which the ribs are mosl distinctly marked, Plate XVII. Fig. -. presents at 

 first sighl a striking contrast to the stems of the other specimens, and, 

 with the stem of Figure 8, is a good example of the greal variation we 



may find ill the joints of stems of one ami the same species. Neither the 



lower part of the stem of Figure 2, nor that of Figure 8 is known. The 

 only portions of stems which appear to form pans of a single stem are the 

 fragments figured in Plate XVIII. Figs. 2. 7. 8, 9, which probably belong 



to the same calyx, and were part of a stem from twenty to twenty-two 

 inches in length, Figure 2 fitting into the calyx of Figure 1. The parts 

 in Figures 7 ami S form a, piece ol the stem intermediate between it and 

 that figured in Figure 'J, nearer the base 



In the upper part of the stems of all the specimens Hat rings are inter- 

 calated between the rings with ribs, and form, as it were, a base upon 

 which the wider-ribbed rings rest. See Plate XVII. Figs. 4. 0, 11 ; Plate 

 XVIII. Figs. 3", 4\ These ilat rings become wider in proportion as they 

 are distant from the calyx ; compare Plate XVII. Figs. 4 to 7. of one 

 stem in which they gradually pass into rings all of which are ribbed, as 

 they are in Plate XVII. Fig. 2, at the lower end of the pari of the stem 

 figured. In the stem figured on Plate XVII. Figs. S. 10, the Hat rings 

 are continued farther from the calyx, while in the stem figured on Plate 

 XVIII. Fig. 2. they extend bul a short distance from the calyx, and soon 

 pass into rings Plate XVIII. Fig. 5°) but slightly ribbed, coming below a 

 part of the stem in which there is only an occasional ring found with a 

 slight rib, or projecting beyond the general outline of the stem i Plate XY1II. 

 Fig. 4 b ). It is probable that Figures 12 and 13 of Plate XVII. formed a part 



* If we may judge 'of the length of the stem of Calamocrinus from that of s fossil species of 



Apioerinida> of which the stem lias 1 n found complete, the length given above is probably a moderate 



estimate. The stem of Guettardierinus dilatatus was about thirty-five inches in length : that of Apio- 

 crinus Roissyanus, thirty-six inches; of Apiocrinus elegans, about twenty-eight inches. In Apioerinus 

 Murchisonianus the stem was somewhat stouter, and not more than twenty-four inches long ; in Mil- 

 lericrinus simplex the stem is thirty-six inches: in Millericrinus polydactylus the known stems vary 

 from twenty to thirty inches, and in M. gracilis the stem was about thirty-two inches, in Millericri- 

 nus Pratti, of which Carpenter thinks the extremity of the stem was not fixed, the length of the stem 

 was probably more than 50 millimeters. 



