214 PROCEEDINGS OF THE ACADEMY OF [1881. 



as those upon the test. The ridges in these cases are evidently 

 the impressions of rudimentar}* grooves, indicating that the plates 

 at that stage were provided with ambulacral furrows like regular 

 arm plates. The}' also had pinnules attached, which like the arm 

 plates were by the growth of the animal absorbed into the calj'x. 

 The fixed pinnules, which Wetherb}- describes in Glyptocrinus 

 Piichardsoni, Cincinnati Soc. Xat. Hist., 1880, and which we found 

 also in Gl. decadactylus and Reteocrinus O^Xealli, confirms our 

 views as to the mode of growth of the Palffiocrinoid, and throws 

 light upon the palasoutological development of Crinoids generally. 

 The number of secondary radials varies considerabl}' with age. 

 In Reteocrinus O'Nealli we have observed as many as seven, but 

 the number may be even more in some cases ; and on the other 

 hand we found in some younger specimens onl}' three or four. 

 The first and second of these plates, and the third and fourth 

 seem to have been united b}' syzygies, at least the first and third 

 bear no piijuules, while beyond the fourth pinnules are given off 

 regularl}' from alternate sides as in the free arms. The proximal 

 pinnule is given off toward the outer side of the ra^y, or, which is 

 the same thing, toward the iuterradial area, the next one toward 

 the interaxillary space. The plate which gives rise to the first 

 pinnule has almost the form of a bifurcating plate, but instead of 

 supporting radials of a higher order, it bears on its inner sloping 

 side a tliird secondary radial, and on the outer a stout pinnule. 

 The first fixed pinnule is highl}' elevated above all other plates of 

 the interradial space, is rounded like the radials, and almost as 

 conspicuous. In one of our specimens it consists of five plates, 

 three of which are soldered into the bod}^, and the fourth appar- 

 ently free. The fixed plates are nearly as strong as the radials 

 and may be easily taken for them, having lik6 them winged exten- 

 sions by which the}' are laterally connected with the interradial 

 plates. The upper joint is much smaller and constructed like the 

 joints of the free pinnules. The second pinnule has only two 

 joints in the body, the third but one, which in either case are 

 larger than any of the free joints, but which already attain some- 

 what more the aspect of regular pinnules, and are gi^-en off in a 

 similar manner. In a specimen of Glyptocrinus Richardsoni, 

 kindl}' loaned to us b}' Prof. Wetherby, the first fixed pinnule is 

 given off from the second plate above the first bifurcation, and 

 consists of seven plates within the body, the third and fourth 



