MOEPHOLOGICAL PAET. 45 



In the Cyathocrinidae the structure at the lower part of the stem is only 

 known in Barycrinus, In Cyathocrinus we have examined the stem to a 

 length of 10 cm.^ and in Parisocrimis to about 18 cm., without finding any 

 traces of lateral cirri. Neither have these been observed, so far as we know, 

 among the Anomalocrinidse or Hybocrinidse ; but in Homocrinus scoparius 

 they occur at the lower half of the stem. 



The stem of Barycrimis is quinque-partite, and enlarges gradually to the 

 root, where its diameter in extreme cases reaches from 30 to 40 mm. The 

 root consists of five main rami, which branch into smaller ones, so located 

 that the longitudinal sutures of the stem bisect the rootlets, and the large 

 central canal, which is sharply pentangular in the stem, becomes elliptic or 

 linear within the branches ; the latter is also the case in Ancyrocriniis, of 

 which we shall speak presently. 



The axial canal is central, and extends to the full length of the stem, 

 giving off branches to the cirri. The main canal is circular, angular, or pen- 

 talobate ; that of the branches sometimes elliptic, the long diameter vertical. 

 If pentangular, the angles are directed radially in dicyclic Crinoids, and 

 interradially in monocyclic, thus alternating with the projecting angles of 

 the stem joints. To this rule, however, there are two exceptions, and, so far 

 as we know, only two. In Pentacriniis, and the monocyclic Glyptocrimis Forn- 

 shelli S. A. Miller, the axial canal has the same orientation as the outer angles 

 of the stem. This is very remarkable, and we shall consider it further in 

 discussing the basals and infrabasals. The canal in some species is quite 

 minute, in others very wide ; while in still others the central canal is sur- 

 rounded by three, four, or five peripheral canals, as in the case of Cupresso- 

 cnmts, in which pentamerous symmetry in the stem is the exception. 



In recent Crinoids the innermost part of the central canal is the internal 

 vascular axis, and consists of five peripheral vessels arranged around a cen- 

 tral one. The former are downward extensions from the chambers of the 

 quinquelocular organ at the base of the calyx, which are connected with the 

 axial vessel of the chambered organ. Whether such vessels also existed 

 in the stem of Palaeozoic Crinoids, of course cannot be ascertained from 

 the fossil ; but that a quinquelocular organ, with upward extensions to 

 the. arms, was present in some of them, is indicated by the structure of 

 Eiipachycrimis, Catillocrinus, and Agassizocriniis, where the inner floor of the 

 basals and radials is apparently perforated. Carpenter ^ thinks it probable 



* Journal of Anatomy and Physiology, Vol. XIL, p. 44. 



