no. 1845. ON THE CRINOID GENUS MAR8UPITE8— CLARK. 653 



central plates are the equivalents of the entire apical system (the 

 dorsocentral plus the columnars) of the developing Antedon. 



There is additional evidence that Marsupites never at any stage 

 possessed a stalk, nor did Uintacrinus. This evidence is purely 

 circumstantial, but appears to be none the less good. The enormous 

 range of Uintacrinus socialis is well known, and recently Marsupites 

 has been shown to have a range equally as extensive. Now we find 

 among the jellyfishes forms which are purely pelagic and other 

 forms which are fixed for varying periods. The extent of the dis- 

 tribution of these different types is very varied, the pelagic species 

 having the greatest and the longest fixed the least range. When we 

 compare the distribution of Marsupites and Uintacrinus with that of 

 the recent jellyfish we find that the parallel is distinctly with those 

 types which are exclusively pelagic and pass through no fixed stage, 

 and we therefore appear to be justified in assuming that Marsupites 

 and Uintacrinus, like them, were always, at all stages, free swimming. 



Marsupites has large orals, and the arms are attached to a com- 

 paratively small portion of the distal border of the radials. Both 

 these features are characteristic of the young Antedon, as well as of 

 the young of all other genera in which the young have been observed. 

 The orals undergo a metamorphosis just as do the underbasals, 

 basals, and radials; but this metamorphosis merely takes the form 

 of gradual resorption. In general, the resorption of the orals is 

 correlated with the metamorphosis of the basals in the comatulids, 

 as exemplified by Antedon. It would be presupposed, therefore, 

 that, were we to discover a comatulid with persistent unmetamor- 

 phosed basals, it would also possess persistent unmetamorphosed 

 orals. 



Correlated with the presence of orals and unmetamorphosed basals 

 in the young Antedon, we find the arms occupying only a small por- 

 tion of the distal border of the radials; and therefore the same feature 

 in Marsupites occasions no surprise. 



Mr. Frank Springer first pointed out the correspondence between 

 the structure of Uintacrinus and that of the comatulids, in particular 

 to those belonging to the Comasteridse. Uintacrinus has the same 

 globular float-like body as Marsupites, but it is differently formed; 

 Uintacrinus has progressed much farther along the plrylogenetic 

 comatulid path; both agree in having a centrale instead of a centro- 

 dorsal and in the possession of underbasals, though these are not 

 always present in Uintacrinus. They should, therefore, be united 

 in the same group, a group parallel to those which I have called 

 Oligophreata and Macrophreata. 



Uintacrinus has an eccentric mouth; if we can judge from the 

 analogy with the eccentric mouth of most of the Comasteridse, it 

 also had a many-coiled digestive tube. The long digestive tube of 



