CALAMOCRINUS DIOMED^. 47 



tlie base, in Avhich the riii^-s have become absolutely discoirlal, and that 

 in which the rings are 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 XVII. Figs. 12, 13, 14), before they become rings with 

 the convex outer outline of the lower part of the stem. The specimen in 

 which the ribs are most distinctly marked, Plate XVII. Fig. 2, presents at 

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

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

 may find in the joints of stems of one and 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 wliicli appear to form parts 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 and 8 form a piece of the stem intermediate between it and 

 that fitjured in Figure 9, nearer the base.* 



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

 calated between the rings with ribs, and form, as it were, a ba.se upon 

 which the wider-ribbed rings rest. See Plate XVII, Figs. 4, 5, 11; Plate 

 XVIII. Figs. 3", 4'\ These flat 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 part of the stem 

 figured. In the stem figured on Plate XVII. Figs. 8, 10, the flat rings 

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

 XVIII. Fig. 2, they extend but 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 (Plate XVIII. 

 Fig. 4"). 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 Calaniocriniis from that of some fossil species of 

 Apioci-iuidse of which the stem has been found complete, the length given above is probably a moderate 

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

 crinus lloissyanus, thirty-six inches; of Apiocriuus elegans, about twenty-eight inches. In Apiocriniis 

 Murchisonianiis the stem was somewhat stouter, and not moi-e than twenty-four inches long ; in Mil- 

 lericrinus siinplfs the stem is thirty-six inches; in Millericrin.is polydactylus the known stmis 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 oO millimeters. 



