MORPHOLOGICAL PART. 63 



monocyclic, and the uppermost stem joint as the last formed plate of the 

 stem. But he seems to have changed his opinion afterwards, for in a letter 

 to us, dated November 28, 1890, he writes as follows: "I have spent this 

 morning studying my material of Rhkocrims, including some fresh specimens 

 which I found among my father's collection, and I conclude that you are 

 right in considering the top-stem-joint as a centro-dorsal hke that o^ Bour- 

 gueticrinus and the Apiocrinid^. It is, however, always the smallest, i. e., 

 thinnest joint of the stem. But it is distinctly marked into ^nq fossae for the 

 basals by radial ridges, and this is sometimes very apparent in the younger 

 individuals. See Chall. Rep. Plate X. Figs. 7 and 8. It is more marked in 

 E. Rawsoni than in R. lofotensis. The pentagonal space in the centre, Plate 

 X. Fig. 5, is nothing but the axial canal." He then continues ; " Bathycrinm 

 is a very different form, with its very numerous thin joints at the top of the 

 stem (see Plates YII. and Yllla), and I have been thinking for some time 

 past that it must be removed from the Bourgueticrinidee and made the type 

 of a new fxmily. The ten arms, and the trifascial articulation are also good 

 characters, as the latter replaces the syzygies oi BUzocrinusy 



Except in one point, we fully agree with this. Examining Plate X of 

 the Challenger Eeport, we find in Bhizocrinus the space within the basal ring 

 very different from the axial canal in the stem joints (see our Plate VI. Figs. 

 la, h), the former being fully twice as large, and pentangular, while the canal 

 is oval. The space between the basals is radially disposed, as in the Apiocri- 

 nid^, and we believe that Bhkocrinus is also pseudomonocyclic. Its structure 

 is altogether different from that of Bathycrimis and Ilyocrinus, which in our 

 opinion are true monocyclic forms. They have no centro-dorsal, and the 

 uppermost joint is the last formed plate of the stem. The open space within 

 the basal ring is interradially disposed, and has the form and size of the 

 stem canal. 



Our observations on the Apiocrinidae led us in 1885^ to the conclusion 

 that most of ih^ Neocrinoidea may have possessed rudimentary infrabasals in 

 their larval state. This rather startling statement was unfavorably received 

 by Carpenter, and severely criticised by him.f He held at that time that 

 with the exception of Encrinus, Extraerinus, Marsupites and TJintacrinus, all Meso- 

 zoic and recent Crinoids were monocychc. His objections, however, did not 

 seem to us convincing, and in Section II. Part III. of the Revision, pp. 294- 



* Revision, Part III., Section I., pp. 8, 71. 



t Bibliogr. Notices. Ann. and Mag., November, 1886, p. 408. 



