:il2 PROCEEDINGS OF THE ACADEMY OF [1881. 



rootlets may have had respiratory functions by introducing water 

 into the bod}'. 



In adult specimens of ActinocrinidiB and Rhodocrinidaj the 

 column was long. We have never seen its full length, but have 

 in several instances traced it three to four feet without seeing 

 either root or body, and we suppose that it was in some genera 

 very much longer. 



Of Plati/cri7ius, however, we have examined five complete speci- 

 mens measuring from the tips of the arms to the extreme ends of 

 the fine rootlets from t to 27 inches — the latter in a large species. 

 In all these specimens, the column gives off for some distance 

 large lateral branches, which decrease in size toward the end of 

 the root, each one with irregular branches which divide again and 

 terminate in hair-lilie tubes. We never saw a Platycrinus in 

 which the root was flattened, as in some of the Actinocrinidae, 

 and it seems possible that the crinoids of this genus only grew 

 on a soft bottom, or possibly floated about with their column like 

 an anchor. The same was evidently the case in the genus Glyp- 

 tocrinus, in which the column was short, tapering to almost a 

 needle's point, without lateral branches. 



9. Mode of Growth and Pal^ontological Development. 



In the Pentacrinoid larva of Antedonj the calyx is composed 

 chiefly of very distinct, rather large basals, alternating with which 

 are five dots, which represent minute radials. The crinoid at this 

 stage consists only of five, columnar joints, the large basals, the 

 rudimentary radials, and of five large oral plates which cover the 

 entire peristome. The succeeding radials, at first unrepresented, 

 develop afterwards, and the arms make their appearance at a 

 much later period. 



Of the Palaeocrinoids, the first stages are, of course, unknown, 

 all the specimens we have discovered— even the very youngest — 

 being already provided with arms, and hence were considerably 

 advanced in the scale of growth. It can be ascertained, however, 

 by a comparison of larger and smaller specimens, that their mode 

 of growth must have been similar to that of Antedon. In the 

 smaller, and as we consider them, younger specimens, the basals, 

 compared with the other ])lates, are much larger, being almost the 

 same size as in mature individuals. Next in size are the first 

 radials, which are larger than the second and third. In the inter- 



