62 CATALOGUE OF THE BLASTOLDEA. 



of ambulacra on which these plates are very well developed, as in Plmnoschisma 

 nobile, P. Archiaci, and P. Verneuili (PL XI. fig. 4 ; PL XIV. figs. 6, 9). They 

 appear to be absent, however, in P. caryophyllatum and in P. acutum (PL XIV. 

 figs. 3, 11), in Codaster and in Orophocrinus (PI. XI. fig. 8 ; PL XIII. figs. 14, 16; 

 PL XV. figs. 7, 14), except perhaps in 0. Orbignyamis (PL XI. fig. 10), and also in 

 Cryptoschisma (PL V. figs. 23, 24 ; PL XIII. fig. 20), all types which are devoid of 

 hydrospire-pores ; while in Pentremitidea, Granatocrinus, Mesoblastus, and Sckizo- 

 blastus they have very much the same relation to the hydrospire-pores as was described 

 by Eoemer in Pentremites (PL IV. figs. 12, 15 ; PL VIII. figs. 5, 11, 15, 21 ; PL IX. 

 fig. 16; PL X. figs. 1, 3). In the latter type (PL I. figs. 1-3) the outer side plate 

 rests upon the proximal edge of the handle of the side plate, so as to form the distal 

 edge and more or less of the inner margin of the corresponding pore. The same 

 is the case in Mesoblastus Sotverbyi, Granatocrinus ellipticus, and G. orbicularis 

 (PL VIII. figs. 5, 21 ; PL IX. fig. 16), in all of which types the plates are relatively 

 larger than in Pentremites. In Granatocrinus campanulatus and in Schizoblastus 

 Rofei, however, the side plates are at the inner side of, rather than behind, the 

 corresponding pores (PL VIII. figs. 11, 15) ; while in Pentremitidea the side plates 

 are without a handle, and sometimes do not extend much beyond the lancet-plate on 

 which they rest, so as to meet the sides of the sinus. The result is that both pores 

 and outer side plates are relatively large (PI. IV. figs. 12, 15 ; PI. X. figs. 1, 3). 



Notwithstanding the fact that Eoemer' s description of the outer side plates has 

 been accepted and confirmed by all subsequent writers on the Blastoids, Hambach 1 

 has asserted that they are merely the remnants of collapsed tentacles, explaining that 

 by this term he meant " the soft and membranaceous organs such as occupy the pores 

 of the ambulacral field in Echinoderms." The only argument which he offered in 

 support of this doctrine is that " the interior circumference of a poral opening is 

 lined with a membranaceous integument." Even supposing this to be the case, we 

 do not see how it proves that relatively large and solid structures, such as the outer 

 side plates of Granatocrinus orbicularis, Pentremitidea Lusitanica, or P. similis 

 (PL IV. fig. 15 ; PL IX. fig. 16 ; PL X. figs. 1, 3), are the collapsed remnants of 

 soft and membranaceous tubes like the ambulacral tentacles of other Echinoderms ; 

 while the fact that outer side plates occur in at least three species of Phamoschisma 

 (PL XL fig. 4 ; PL XIV. figs. 6, 9), although the genus is entirely devoid of 

 hydrospire-pores, is a strong objection to Hambach's theory, to which we shall refer 

 again further on. 



1 Trans. St. Louis Acad. Sci. 1880, vol. iv. no. 1, pp. 151, 152. 



