4 ANNALS NEW YORK ACADEMY OF SCIENCES 



species. In form, the arms arc cylinflrical at the base, but at a distance 

 from the base varying from the third to the tenth plate, they become flat- 

 tened laterally, and the individual plates are elongated, producing a 

 marked expansion of the arm at about half its height which may be taken 

 to represent the adult stage. Beyond this, the arm tapers- gradually to a 

 point, at the same time becoming more nearly circular in cross section 

 than at its middle portion. In the growth of the crinoid arm, new plates 

 are formed at the tip, and these small, nearly cylindrical plates are in an 

 immature condition. Their resemblance in fonn to the plates near the 

 base of the arin probably indicates that they are passing through a stage 

 comparable to an early stage in the development of the entire arm. That 

 such localized stages occur in other genera has already been pointed out 

 by Grabau.- 



Immature plates were observed only in Cactocrimis prohoscidalis and 

 C. haccaiun. Others of the species studied had the arms strongly in- 

 curved and the tips concealed by the matrix, except in the C. multi- 

 hrachiatns series where the arms were imperfect at the ends. 



Each plate of the arni of (\ prohoscidaJis bears a distinct transverse 

 ridge running the entire widtli of the plate and situated about one-third 

 of its height from the upjier margin. The ornament a])pears on early 

 plates, at distances from the base differing somewhat in different speci- 

 mens, and continues to the extreme tip of the arm. The proximal pin- 

 nules, as in other species of the genus, bear strong overlapping spines. 



C^olumn cylindrical. 'I'he proximal nodals project but slightly beyond 

 the internodals, but at a distance of about 20 millimeters from the calyx, 

 the nodals have twice the diameter of the internodals and have their 

 margins extended into a thin, knife-like edge. At a distance of 85 milli- 

 meters from the body, the n\nnber of intercalated plates has increased 

 •Qntil there are seven between successive nodals. and at this point the 

 nodals have blunt margins projecting but little beyond the internodals. 



Tegmeii moderately high, covered with numerous nodose plates. Anal 

 tube long and slender. 



Horizon and locality: T.owcr Bnrlinfitou liinostone, Burlington, Iowa. No. 

 415. Musouin of ConiiiMrative Zoology oollection. 



' Cactocrinus baccatus sp. nov. 



Plate I. fig. ."i: plate TT. figs. .3, 4. 4a, 4?) 



Calyx similar to that of CuctdcririuK prohnxridaUa in form. Rasals variable 

 in size, .sometimes minute with the calyx resting upon the radials, sometimes 

 as large as in Cactocrinu.<< prohn-tcidaliH. 



»A. W. Grabac : Amer. .lonr. Sii.. 4th ser.. Vol. 16, pp. 289-300. 1903. 



