40 GEOLOGICAL MEMOIRS. 



orifice, and therefore nothing that can mark them as belonging to 

 the Cystidea. M. Eichwald conjectures, and with some probability, 

 that they may be coralline bodies, perhaps Favosites {Calamopora) 

 resembling the specimens described by M. Pander (tab. 29 of his 

 book, fig. 4, 5, 6). 



The Cystidea belong unquestionably to the most ancient for- 

 mations of the earth's surface, to the Silurian strata of the Palaeozoic 

 period. In more recent formations nothing analogous to them has 

 hitherto been met with, and still less do they appear in the existing 

 creation. That they form the extreme verge of an entire group of 

 Radiaria, is shown by these ancient and isolated examples ; and the 

 Caryocrinite indicates in a most singular manner in what way the 

 passage from Cystidea to Crinoidea may have taken place. As 

 soon as this happened and arms were developed, this group of animals 

 multiplied itself immediately into a vast variety of forms, and during 

 the carboniferous period appears to have attained its maximum. 



The closed cup which in Cystidea enwrapped and concealed 

 the whole animal then gradually disappeared, and at length, as in 

 Pentacrinus, is hardly more than a basis upon which the soft parts 

 were supported. 



In the rocks of the Oolitic series, the multitude of genera dimi- 

 nished rapidly, while the distribution of the separate species in- 

 creased in almost the same proportion ; and at length, in the upper 

 oolites, we find that the animal had broken loose from its pedicle, 

 and, in the form of Comatula, appears as a free swimming animal. 



Apiocrinites ellipticus is almost the only true Crinoid of the chalk 

 which connects itself with the older forms, and Pentacrinus Caput 

 Meduscc, which still remains, ofi'ers but a faint shadow of the noble 

 and beautiful sea-lilies of the ancient seas. But in the Pentacrinus 

 europceus {Comatula rosacea)^ discovered in 1827, we seem to have 

 this whole change brought about in the transmutations of a single 

 species. Miiller {Pentacrinus , p. 7) thus expresses the modifica- 

 tion : — " The younger specimens appear like little clubs {CysUdea) 

 fixed by a spreading base, and send out from their summits a few 

 pellucid tentacula. No portion of the hard part is visible, except 

 an indistinct appearance of the cup. At a more advanced stage 

 the arms begin to appear, at the same time with the prolongation of 

 the stem, and the pinnules are more prominent and become visible 

 as cirrhi, on which the arms elongate. It is then a Crinoid. When 

 full-grown the animal disengages itself entirely from its stem, be- 

 coming a Comatida, and now swims freely in the sea without being 

 interfered with in its further development." 



