56 CATALOGUE OF THE BLASTOLDEA. 



groove is visible on its upper surface (PI. IV. fig. 15; PI. V. figs. 3, 4, 19; PI. VI. 

 fig. 13 ; PL XI. fig. 4 ; PL XIII. fig. 19 ; PL XIV. figs. 5-7, 9, 11). This condition 

 may likewise occur at the ends of the ambulacra in Granatocrinus (PL XI. fig. 14), 

 Codaster, and apparently also in Pentremites and in Cryptoschisma (PL I. fig. 2 ; 

 PI. XIII. fig. 20). 



C. The Side Plates. 



The plates to which we have given this name are those which were designated as 

 " Porenstucke " by Roemer in his classical monograph on Pentremites 1 . In this genus, 

 and also in Pentremitidea, Schizollastus, and Elceacrinus, they come into close relation 

 with the hydrospire-pores along the margins of the ambulacra, as was first indicated 

 by Troost -, though not clearly so (PL I. figs. 1-3 ; PL III. fig. 3 ; PL IV. fig. 14 ; PL X. 

 fig. 1 ; PI. XVIII. figs. 17, 18). The same is the case in Mesoblastus, Granatocrinus, 

 and Cryptoblastus, though in all these genera there is a second set of internal pores 

 which are formed between the hydrospire-plate and the wall of the radial sinus, and 

 are smaller than the external series (PL IV. fig. 4 ; PL VI. fig. 10 ; PL VII. fig. 15 ; 

 PI. VIII. figs. 15, 20; PL IX. fig. 16 ; PI. X. figs. 11, 12). But for the presence 

 of this internal series the external pores, which are merely gaps between the outer 

 ends of successive side plates, would not be of much use. They are altogether absent 

 in Codaster, Phamoschisma, Cryptoschisma, and Orophocrinus (PI. V. figs. 23, 24 ; 

 PL XI. figs. 4, 8, 10 ; PI. XIII. figs. 14, 20 ; PL XIV. figs. 3, 6, 9, 11, 18), although 

 side plates are present and in some cases reach a considerable relative size. In spite 

 of these facts, however, Roemer's name (" pore-pieces ") has continued in use, and 

 may even be found in descriptions of species which are expressly stated to have no 

 marginal pores to the ambulacra. Meek and Worthen 3 have expressed their belief 

 that these pore-pieces are " recumbent arm-pieces similar to those of m;my Cystoidea," 

 and Messrs. Wachsmuth and Springer 4 seem to share this belief. This may or may 

 not be the case ; but at any rate, it seemed to us unadvisable to be continually 

 noticing the presence of arm-pieces in Echinodermata which are nothing if not arm- 

 less. We have therefore changed the name " pore-pieces " to " side plates," and 

 likewise prefer to substitute the word "outer" for "supplemental" in describing the 

 supplemental pore-plates which Roemer discovered in Pentremites and Elatacrinus. 



The relations of the side plates to the lancet-plate vary very greatly among the 

 different species of Blastoids. In Orophocrinus Orhignyanus (PI. XL fig. 8), Crypto- 

 schisma Schulzi (PI. XIII. fig. 20), Phoenoschisma caryophyllatum (PL XIV. fig. 3), 

 and in all the typical Pentremites with more or less petaloid ambulacra (PL I.), 



1 Archiv f. Naturgeseh. 1851, Jahrg. xvii. Bd. i. p. 334. 



2 Trans. Gool. Soc. Pennsylv. 1835, vol. i. pp. 226, 227. 

 - 1 Report Geol. Survey Illinois, 1873, vol. v. p. 4(13. 



4 Revision of the I'ala;oerinoidea, Tart I. 1879, p. 11. 



