484 FRANK SPRINGER 



a synonym of Ichthyocrinus, may now be assigned a definite place in 

 the analysis of the genera. Thanks to the courtesy of Dr. Bather^ 

 I have recently had the opportunity to examine the type specimens, 

 now in the British Museum; and they demonstrate very clearly the 

 generic distinctness of this form. It has the regular dicyclic base of 

 the Flexibilia, with 5 BB and 3 IBB — the latter more or less atrophied, 

 or resorbed by the very large axial canal ; and it has a series of large 

 anal plates, completely filling the posterior area, together with a small 

 development of interbrachial plates. It has the habitus of the 

 Ichthyocrini, and stands close to Parichthyocrinus, from which, 

 however, it is well distinguished by the anal structure. 



I am also now enabled, by the aid of Liljevall's drawings and 

 some interesting specimens in the British Museum, to treat more 

 definitely the genus Pycnosaccus, which was formerly placed as a 

 probable synonym under Lecanocrinus. It has fairly large inter- 

 brachial areas, which are apparently without well-defined plates, such 

 as are in Anisocrinus, but were evidently filled by small, irregular 

 plates which are not preserved in any of the specimens thus far seen . 

 The calyx as observed is strong, and much wrinkled or folded exte- 

 riorly. It also frequently has but a single primibrach. 



Cleiocrinus, from the Lower Silurian of Canada, which was before 

 arranged with this division of the Flexibilia, may now be left out of 

 it, except as a probable transition form. From an investigation I 

 have recently made of all the known material, this proves to be an 

 even more extraordinary and anomalous genus than Calpiocrinus, 

 being probably an intermediate form between the Camerata and the 

 Flexibilia. It has the pinnulate arms and five infrabasals of the 

 dicyclic Camerata, combined with the pliant calyx, with plates united 

 by loose suture, of the Flexibilia.^ 



I exclude from the list of Flexibilia the genus Rhopalocrinus, 

 which may be considered as an intermediate form between the Flexi- 

 bilia and the Inadunata. It has a strong ventral tube, rising high 

 up between the arms. It lacks the pliant calyx of the former group, 

 but rather resembles a dicyclic Symbathocrinoid, and would readily 

 fall under the Inadunata but for the presence of a shghtly developed 

 interbrachial system. 



I Memoirs, Museum of Comparative Zoology, Harvard, Vol. XXV, Part 2. 



