354 PROCEEDINGS OF THE ACADEMY OF [1885. 



little rootlets, which gradually taper, spreading out horizon- 

 tally. 



Eucalyptocrinus is one of the most perplexing genera, especi- 

 ally by reason of its peculiar ventral structure. The only ventral 

 plates aboul which there seems to he no doubt are those of the 

 firsl ring, which have been designated by all writers as large inter- 

 radials and interaxillaries, i. e., interdistichalia. More dubious 

 arc those of the second ring, which partly cover the peristome. 

 They fit with their projecting angles into the ten re-entering angles 

 formed by the sloping sides of the preceding plates. The plates 

 of the one ring practically alternate with those of the other, for 

 by bisecting the two smaller plates, and dividing the larger ones 

 into three pieces, we obtain ten nearly equal plates, alternately 

 arranged, thus proving that the plates are not in part interaxil- 

 laries; but what are they? We doubt if they are calyx inter- 

 radials; the fact that there are four plates is certainly a very 

 serious objection. By dividing the plates among the five inter- 

 radii, some of the pieces would be distributed among different 

 areas. Another interpretation seems to us more probable, and 

 offers at t he same time an explanation of the plates in the third ring. 



The proximals and the oral plate, in all Palaeocrinoids with 

 nearly central anal tube, are pushed to the anterior side, and the 

 oral plat i- and the two smaller proximals constitute actually a part 

 of the tube of which the four larger proximals form the base. We 

 think the ease is very similar in Eucalyptocrinus, but here, owing 

 to the strictly central position of the anal tube, not only one of 

 the proximals, but also the oral plate is penetrated by the anal 

 passage, and divided into two parts. This, if correct, suggests 

 thai in Eucalyptocrinus the four plates of the second ring repre- 

 sent the four large proximals, a view which seems to be confirmed 

 by the peculiar arrangement of the plates in the third ring, in 

 which we consider that the two smaller ones represent the two 

 smaller proximals, while the two larger pieces, which rest upon 

 all plates of the second ring, are equivalent to the oral plate. 

 This would further suggest, that the ten plates in the fourth ring 

 :irr extravagantly developed anal plates. 



Geological position, etc. — Eucalyptocrinus is one of the leading 

 genera of the Upper Silurian, and it occurs in America and 

 Europe. A single species is known from the Devonian. 



The following species have been described: — 



