NO. 184G. ON CERTAIN ELEUTHEROZOIC PELMATOZOA—KIRK. 47 



diameter likewise indicate that the break took phice well up on the stem. 

 Subsequent to the breaking off of the column, there was a secondary 

 deposition of stereom over the fracture. Lime continued to be 

 deposited until a knob of very considerable size was formed at the end 

 of the stem. Such a knob is quite irregular in shape and shows no 

 signs of cementation to the bottom. It apparently served as a bal- 

 last or drag for some freely swimming crinoid. 



Such structures recall the knobs formed at the distal extremities of 

 the columns of Metacrinus and Isocrinus, as reported by Carpenter 

 and noted above. In the latter cases, however, the deposits of lime 

 are of no very great size, little more than pluggmg the axial canal, and 

 smoothly rounding off the end of the column. The curious object to 

 wliich Barrande (1887, PI. 4, III, figs. 1-6) gives the name Neocys- 

 tites hohemicus seems quite certainly to be such another distal knob 

 formed over the fractured surface of a ruptured column. The stem 

 is unquestionably, I believe, that of a crinoid. 



Herpetocrinus. — The genus Herpetocrinus is here held as a detached 

 form on the authority of Bather (1893 and 1900). In this genus the 

 column, which is a most remarkably modified organ, is coiled about 

 the body of the crmoid, the coiling taking place in a single plane. 

 Along a very considerable portion of the stem there are borne two 

 rows of cu'ri, which are given off toward the inner portion of the coil. 

 In Herpetocrinus as found, the crown lies entirely concealed between 

 these rows of cirri. 



It is evident under normal living conditions that the crinoids did 

 not mamtain this close coiling of the column, wliich was probably 

 only assumed in case of irritation. It is likewise obvious that the 

 plane of coiling could scarcely be that of the sea bottom. We 

 must then assume when the anunal was temporarily attached that 

 it grasped some object with the cirri of the distal portion of the 

 column, an erect position being maintained. At special tunes the 

 anunal could retract and assume a closely coiled position. The 

 advantages of this coiling are not on the whole immediately obvious. 

 A somewhat similar structure is to be observed among the Camerata, 

 in the case of Camptocrinus, so the modification appears to have some 

 good reason for its existence, divergent from the normal tendency 

 though it be. It can scarcely be considered as purely protective, for 

 why should one genus acquire such highly specialized protective 

 structures when the associated organisms apparently have no need for 

 anything of the sort, and when the physical conditions of environ- 

 ment appear to be quite normal ? 



It seems probable during the greater portion of the life of this form 

 that a detached existence was maintained, and that attachment 

 when effective w^as but temporary, and brought about through the 

 clasping action of the cirri. It is interesting in this connection to 



