CALAM0CRIN1 S DIOMED E 61 



the main stem itself gradually becoming reduced to the size of one of the 

 branchlets, much as in Rhizocriuus. The column of this genus is noted 

 for its large axial canal. 



In some of the figures given l>\ Meek of the stem of the Bame genus, 

 a few of the upper stem joints appear to be somewhal thinner than the 

 others, while in other cases thick and thin joints alternate (Geol. Survey 

 ofOhio, Palaeontol., Vol. I. Plate I |. 



In the upper part of the stem of Heterocrinus, a rding to the figures 



given by Meek and Wortheu, the llai joints of uniform height taper quite 

 rapidly (Geol. Survey of 111., Vol. III. Plate I . 



In the second volume of the Geological Survey of Illinois. Meek ami 

 Worthen figure the upper part of the stem of Onychocrinus as made up 

 of very thin Hat joints, the stem tapering quite rapidly and being composed 

 of flattened joints of greater height (Plate 17. Figs. :;. 7). 



The column of Glyptocrinus consists of alternately thick and thinner 

 pieces, the former projecting beyond the latter. 



.Meek has also figured* the upper part of the column of an interesting 

 specimen of Heterocrinus jnvenis. in which young joints are intercalated 

 between every two of the older joint-!. Of these he says, " Column . . . 

 composed of moderately thin disks, between each two of which are inter- 

 calated, for some distance below the body, five small pieces, ranging ex- 

 actly on lines with, and corresponding in size and form to. the subbasal 

 pieces at the connection of the body with the column ; further down these 

 intercalated pit m-< seem to coalesce and form disks like the others."^ 



In a fine stem of Megistocrinus nobilis, W. & S. (Geol. Survey of 111., 

 Vol. VIII. Plate XVI. Fig. G), the rings alternate from the very top. with 

 projecting and receding joints. The same is the case in the stem of 

 Dorocrinus (Vol. VIII. Plate XVII. Fig. G), while the upper part of the 

 stem of Actinocrinus Arnoldi, W. & S. (Plate XVII. Fig. 10), is made up of 

 joints with angular sides, nearly of the same diameter, slightly tapering 

 from the top. 



In some other species of Poleriocrinus, P. occidentalis (Geol. Survey 

 of 111., Vol. VII., Plate XXVII. Fig. 2) and P. coxanus (Fig. 1), the upper 

 part of the stem, made up of uniform joints, very soon passes into a 

 structure made up of narrow ilat joints alternately higher and flatter. 



* Geol. Survey of Ohio. Paleontology, Vol. I. Plate 1, Fig. 3 a. 

 t Ibid , Vol. I p. 11. The Italics are mine. 



