44 THE VOYAGE OF H.M.S. CHALLENGER. 



Pentacrinidse and Comatulse ; and I see no reason to believe that the minute interradials 

 of Reteocrinus are in any way different from those of the Neocrinoids. But I regard 

 them as perisomic phxtes continuous with those of the disk above, which was in no sense 

 a " vault " like that of the Actinocrinidse. Meek's figure of Reteocrinus nealli ' 

 illustrates this point admirably, and after examining disks like those of Pentacrinus 

 ivyvillc-thomsoni, Pentacrinus alternicirrus, Pentacrinus naresianus, and Pentacrinus 

 mollis, together with similar disks in numerous Comatulas (PI. XVII. fig. 6 ; PI. XXVI. 

 figs. 1, 2; PL XXX. fig. 2; PI. XXXIII. fig. 7; PL LIV. fig. 10; PL LV.), and also 

 (thanks to the kindness of Mr. AVachsmuth) that of Reteocrinus nealli, I find it difiicult 

 to believe that the so-called vault of Reteocrinus was anything but the true oral surface 

 of the animal. 



Miller's genus Xenocrinus " is in this respect essentially similar to Reteocrinus. 

 " The azygos area is remarkably large and covered in the central part by a vertical series 

 of plates having about the same size as the regular radial series; and upon each side of the 

 vertical series there is a depressed area covered by small plates having a tubercle in the 

 central part, as in the regular interradial areas. There are seven plates, each having a 

 length about twice as great as its width, in the vertical series, from the basal plate, upon 

 which the series rests to the top of the vault. This vertical series is continued to the 

 top of the proboscis, and contains in its entire length more than fourteen plates. It has 

 such strong resemblance to the radial series, except as to the branching at the secondary 

 radials, that the general appearance of the body is that of a species having six radial 

 series." Miller figures the specimen with fourteen plates in the vertical series, and 

 remarks that we learn from it that "the proboscis extends as high as, and probably 

 beyond the extremity of the arms." He also says that the small plates between the rays 

 and their subdivisions " continue over the margin of the vault, and undoubtedly cover it, 

 and also more or less of the long proboscis." I do not see, however, that this so-called 

 but unknown proboscis is anything more than an anal tube covered by j^erisomic plates, 

 us in Extracrinus and so many other Neocrinoids. I also doubt whether Miller is right in 

 stating that the vertical series is continued to the top of the proboscis, for (to judge from 

 his figures) he does not seem ever to have met with a specimen perfect enough to show 

 the top as it is shown in Meek's figure of Reteocrinus nealli.'^ But I think it quite 

 possible that, considering the size of this vertical series, it may have become free at the 

 top of the calyx as the anal appendage of Thaicmatocrinus does (PL LVI. figs. 4, 5), 

 instead of tapering away quickly and ending on the lower part of the anal tube as in 

 Reteocrinus nealli. 



The ventral sac or proboscis of Cyatliocrinus is usually much larger and more 



' Palseoutology of Ohio, vol. i. pi. ii. tig. 3c. 



'^ Description of some New and Remarkable Crinoids and other Fossils of the Hudson River Group, Journ. Cine. Soc. 

 Nat. Hist, vol. iv. pp. 72, 73, pi. i. fig. 3 ; pi. iv. fig. 6. ' Palaeontology of Ohio, vol. i., pi. ii. tig. 3c. 



