192 



ECHINODERMATA PELMATOZOA 



SUB-KINGDOM III 



be noted, are frequently effaced in weathered specimens (Fig. 315, A and E]> 

 Small pit-like depressions, or small tubercles, which are observable on the side- 

 plates, indicate the places where the appendages or pinnules were formerly 



attached. These are 

 \ J^J^L / only exceptionally 



completely conceal 

 the ambulacral fields, 

 and extend upward 

 above the summit of 

 the calyx (Fig. 316). 

 They vary consider- 

 ably in length, even 

 among species be- 

 gub longing to the same 

 genus. 



In most Blastoids 

 the side-plates, or 

 the outer side-plates 

 when such are present, are pierced by marginal pores (or hydrospire pores), which 

 communicate with the hydrospires. The pores are situated at the extreme 

 outer margins of the plates, at the end of the lateral ridges, and alternate in 

 position with the sockets of the pinnules. They are present in all forms, 



FIG. 316. 



a, Pinnule of Pentremites, enlarged ; 

 b, Granatocrinus Norwoodi, O. and S., 

 with perfectly preserved pinnules (after 

 Meek and Worthen). 



Trans- 



Pentremites sulcatus, 

 Carboniferous ; Illinois 

 verse section of calyx at about 1/3 

 the height of the ambulacral fields. 

 X 1 !/2- hy, Hydrospires ; I, Lancet- 

 plate ;" p, Pore-plates ; r, Radials. 



Transverse sections through the ambulacral fields, showing various forms of hydrospires. A, Granatocrinus 

 Derbyensis. B, Granatocrinus Norwoodi. C,*Metablastus lineatus. D, Orophocrinus verus. All sections enlarged 

 (after Etheridge and Carpenter). 



having the hydrospires concealed within the calyx ; but are absent in the 

 Codasteridae, in which the hydrospires are wholly or in part exposed on the 

 outer surface. 



The hydrospires are bundles of flattened, lamellar tubes, extending under- 



1 [According to Wachsmuth these markings are not a mere ornamentation ; but the ridges consti- 

 tute the sides, and the depressions the floors of a series of small ducts leading from the pinnules to 

 the median ambulacral groove. In a number of excellently preserved specimens observed by this 

 distinguished author (Pentremites, Orophocrinus, and Schizoblastus), not only the longitudinal groove, 

 but also the side grooves throughout the entire field were roofed over by alternately arranged, very 

 minute plates, extending all the way to the pinnules. The arrangement of the side ducts, their 

 upward curvature on approaching the main canal, and their relations to the pinnules, leaves scarcely 

 a doubt that they were closed food-grooves serving to conduct nutriment from the pinnules to the 

 mouth. 



It is questionable whether the term " pinnules " is strictly appropriate as applied to the appendages 

 of Blastoids, for while the latter evidently performed the function of arms, it is by no means certain 

 that they discharged the ova, which is the special office of pinnules in Crinoids. The statement that 

 the appendages are frequently biserial does not agree with the observations of Wachsmuth. All the 

 specimens examined by this writer are uniserial, but the ossicles are sometimes sharply wedge-shaped, 

 and interlock to a slight extent from opposite sides, thus simulating a biserial arrangement. TRANS.] 



