474 FRANK SPRINGER 



leaving a sort of central tongue projecting upward; finally, soon after 

 the Crinoid becomes free, they completely disappear. 



The condition presented by the disk of Onychocrinus may be con- 

 sidered to be somewhat approximate to that of the last stage of the 

 Antedon Pentacrinoid before it casts off the stem, and before the 

 orals are finally resorbed (Plate V, Fig. 7). In the irregularity in 

 the size and shape of the orals in these fossils we may perhaps recog- 

 nize some of the different stages of absorption in the Antedon larva 

 as above described. 



We may also compare the morphological condition of our disk 

 with that of P. H. Carpenter's remarkable recent genus Thaumaio- 

 crinus.^ His solitary specimen, of which I reproduce one of his figures 

 (Plate IV, Fig. 6), was very small, probably in a young stage. If we 

 imagine it in a more mature condition, with the orals pushed inward 

 and made relatively smaller by the growth of perisome, and the anal 

 tube more or less enveloped by it, we shall have a disk somewhat 

 analogous to ours. Of course the enormous posterior oral of the 

 Onychocrinus disk does not find a parallel in any of the recent teg- 

 mens. Its pronounced bilateral symmetry is a paleozoic charac- 

 teristic, strongly marked among the Camerata and Inadunata, as 

 well as in many of the Flexibilia. It is possible that the posterior 

 oral is a madreporite, as has been found in many Cyathocrinidse. 

 It seems to be perforated with somewhat scattered pores in several 

 specimens, one of which I figure, twice enlarged (Plate IV, Fig. 4). 

 This may be something like the water-pores in the orals of Holopus, 

 as shown in Carpenter's figure above cited (Plate V, Fig. 8). 



Since obtaining the above-mentioned specimens, I have succeeded 

 in exposing the disk of a specimen of Onychocrinus exsculptus, from 

 Crawfordsville — a thoroughly distinct species. While by no means 

 so perfect, it shows that the structure is substantially the same. I 

 have also obtained another disk of Taxocrinus, from a much later 

 horizon than T. intermedius, which exhibits the same characteristics 

 as the latter species. 



Further Remarks on the Crinoidea Flexibilia 



In a paper in the American Geologist for August, 1902 (pp. 88 ff.), 

 I offered some suggestions looking to the systematic arrangement of 



I Philosophical Transactions, Royal Society, Part III (1883), p. 919. 



