434 SMITHSONIAN INSTITUTION 



The progressive increase in relative elongation of the rami which was noted in the 

 remarks upon O. exsculptus has in this and allied species proceeded far beyond the maximum 

 attained in that species. While on an average of all the species of the exsculptus group 

 the main rays exceeded the rami in length as 1.25 to 1, in the ramulosus group the rays are 

 shorter than the rami by an average of 1 to 2.4. 



The whole facies of the widely spreading rays — suggesting a starfish, with clusters of 

 short arms resembling the talons of a bird — which so strongly arrested the attention of 

 Lyon, is wanting in this species, where the calyx and rays have again the relative proportions 

 of a very elongate Taxocrinus. It may in fact be readily derived from the section of that 

 genus having few interbrachials, like T. macrodactylus, just as the exsculptus form may be 

 derived from such species as T. intermedins, by adding to each the heterotomous arm struc- 

 ture ; and I am by no means sure that from an evolutionary standpoint a division of genera 

 upon these lines would not be the most logical. The difficulty would be in finding a dividing 

 line upon this character in Taxocrinus, where the change from few to numerous interbrach- 

 ials is so gradual. 



The 3 IBr feature is absolutely constant in this species throughout large numbers of 

 specimens ; as is also the 4 IIBr of the first interval, wherein it differs not only from the 

 exsculptus group, but from the other species of this. The tendency is to long intervals 

 between the ramules and between their branches. The ramules are sometimes almost as 

 large as the rami ; they branch frequently and by more or less equal bifurcations as many as 

 five times in very mature specimens, the subordinate branches also branching again. It 

 is difficult in most cases to trace the full length of the ramules, as they are generally covered 

 over by others and by the rami ; but in the magnificent specimens 2 and 3 of Plate LXXII 

 not only this but also the fine terminals of the ray are beautifully shown. 



The arcuate sutures, giving the appearance of patelloid plates between the successive 

 brachials, are more conspicuous in this than in any species of the whole family ; the project- 

 ing lip, and the crescentic socket into which it fits, are unusually thick and deep, so that they 

 do not disappear with ordinary weathering, as in many other species. There is scarcely a 

 specimen in its natural condition in which they are not perfectly plain throughout the entire 

 ray; and it requires considerable grinding before the straight suture is reached. Figure 10 

 of Plate LXXII shows where I have done this on a curved surface of the primibrachs. 



The stem of this species is much longer than in 0. exsculptus, and longer than is known 

 in any other species of the Flexibilia. I have two specimens, not figured, in which it is pre- 

 served for 36 inches to near the root, indicating a length of over three feet in medium-sized 

 specimens. In such a mature specimen as figure 2a it was probably much longer. 



Nothing is known of the tegmen in this species. The condition of the specimens is not 

 favorable for discovering it, as the rays are usually closely folded. Nevertheless I have 

 explored two or three to the bottom of the cup without finding any definite structure except 

 some rather small plates resembling orals ; and I am of the opinion that the perisome was 

 very fragile, and the orals small. There is no sign of such large plates as the posterior oral 

 of the exsculptus group. It is not improbable that we should find here a quite distinct teg- 

 men ; the perisome must have been weak, for among numerous otherwise good specimens 

 we rarely find the anal tube preserved beyond one or two plates. 



From the extraordinary development of iBr in the higher axils (in one specimen to the 

 eighth ramule) there must have been an extension of perisome along the rays such as is not 

 known in any other species of the Flexibilia. 



This species occurs in the same layers with 0. exsculptus, in the great crinoid colony 

 at Crawfordsville, where it is nearly as abundant. The present studies were made from 

 about a hundred selected specimens which show remarkable constancy of characters, there 

 being scarcely any variation among them except that due to age, as shown by the series of 

 figures on Plate LXXII. I figure also a couple of abnormal specimens ; one with the left 



