234 ECHINODERMATA— PELMATOZOA phylum iv 



Metacrinus P. H. Carpenter. Arms dichotomous, multibrachiate ; IBr 

 four to eight in number. The distal portion of the arms bears only 

 rudimentary pinnules. Recent ; Pacific Ocean. 



Hypalocrinus A. H. Clark. Ten arms only, unbranched ; IBr two. The 

 distal portion of the arms bears only rudimentary pinnules. Recent; East 

 Indies. 



Comastrocrinus A. H. Clark. Resembles the preceding, but with more 

 than ten arms, and with the distal edges of the brachials strongly produced. 

 Recent; Indian Ocean. 



Section B. Thiolliericrinids A. H. Clark. 



Column persistent throughout life; hut columnar development ceases after the 

 formation of the first nodal. 



Thiolliericrinus Etallon. Column resembling that of the pentacrinoid 

 larvae of the Comatulids, but greatly enlarged and thickened ; calyx as in the 

 adult Comatulid. Jurassic and Cretaceous ; Switzerland, France, Portugal. 



The genus Thiolliericrinus has been considered both as representing a primitive Comatulid, 

 and a transitional stage between the Apiocrinidae and the Pentacrinidae ; but neither view 

 is correct. The column of Thiolliericrinus is comparable to that of a Comatulid or of a 

 Pentacrinid at the time of the formation of the centrodorsal or of the first cirriferous nodal ; 

 stem development has here abruptly ceased, so that the column has retained its primitive 

 Bourgueticrinoid character, modified only by an increase in size ; but the calyx has continued 

 to develop so as to be comparable to the calyx of the Comatulids, or to the calyx of the 

 more advanced aniong the Pentacrinids. Thus Thiolliericrinus possesses the calyx structure 

 of the adult Pentacrinid or Comatulid, combined with the column structure of the larvae of 

 the same types. It therefore falls naturally between them. 



Section C. Comatulids Fleming (emend.).i 



Column either wanting entirely, or discarded after the formation of the first 

 nodale which remains permanently attached to the calyx. 



While the Comatulids, as already explained, forin a group strictly comparable in 

 phylogenetic value with the Pentacrinids and Thiolliericrinids, this group is 

 wholly disproportionate to those in complexity and extent. Owing to their enormous 

 and cosmopolitan development in Recent seas, the Comatulids require for their 

 Classification further subdivision in a way not applicable to any of the fossil families. 

 The group must therefore be taken as a new unit, divisible into subgroups which are 

 comparable in rank only inter se, and not with subdivisions of similar grade or 

 terminology among the other Crinoids. 



Tribe 1. Innatantes A. H. Clark. 



Pelagic Comatulids in which the basals are not metamorphosed hut form an 

 integral part of the hody wall ; the infrahasals are not united with the central plate, 

 but frequently, through individual Variation, they are absent. There is no evidence of 

 attachment in any hnown material, so that their central apical plate probably repre- 



^ Literature : Müller, J., lieber die Gattung Comatula, etc. Abhandl. Berlin. Akad. 1847. — 

 Ludwig, H., Beiträge zur Anatomie der Crinoidea. Zeitschr. wiss. Zool, vol. xxviii. 1877. — 

 Carpenter, P. H. Report on the Crinoidea. Sei. Eesults Ghali. Exped., xi. and xxvi., 1884-88. — 

 Jaekel, 0., Entwurf einer Morphogenie und Phylogenie der Crinoideen. Sitzber. naturf. Ges., 1894. 

 — Clark, A. H., See titles cited under general discussion. 



