NIAGARA GROtTP. 



CYSTIDEiE. 



233 



There are certain peculiar fossil bodies, which, from their general structure and habit, have 

 usually been arranged with the Crinoidese ; but to which the name of Cystidea; has been given 

 by M. Von Buck*, who regards them as forming a distinct order of Echinoderms, inferior to 

 the Crinoids. They approach the CrinoideES in some of the genera, and depart widely from that 

 family in others. Among the obvious characteristic distinctions we may mention that the genera 

 of cystideans have the entire body more or less spherical, and entirely covered with polygonal 

 plates, except at several points where there exist apertures connected with important functions 

 of the animal. One of these apertures near the summit is the mouth, and near it is an anal 

 aperture or pore ; but the most conspicuous one is the ovarian aperture, which is situated below 

 the summit, on the posterior side of the animal. The arms are either absent altogether, or very 

 much modified in their character, when compared with those of the Crinoidea proper. Instead 

 of originating from the higher plates of the cup, which are gradually changed in form, or the 

 interstices filled with smaller plates, the cystideans are entirely enclosed ; and the appendages 

 representing arms are spread over the summit, originating from near the mouth, and extending 

 down the sides to a greater or less distance ; or represented only by a few oral tentacula. These 

 arms in many species consist of a double series of joints, separated from each other by a 

 groove, and the whole resting in a depression upon the surface of the plates or along their 

 joining edges. These representations of arms appear like a surface ornament, but they are 

 readily separated from the plates, and are shown to be composed of joints of unequal size. At 

 certain points upon these arms there arise jointed tentacula, not very dissimilar to those of 

 some Crinoidea ; so that the surface is ornamented with several rows of tentacula, diverging 

 or radiating from the summit. 



These arms and tentacula are not present in all species : indeed they were at first supposed, 

 by Von Buch, to be destitute of arms altogether ; and some of the species possessing these 

 appendages may have them entirely removed, leaving no positive evidence of their having 

 existed, beyond the shallow groove in which they are imbedded, and even this is sometimes 

 obliteratedf. 



* Uber Cystideen, &c., by Leopold Von Bitch : Transactions of the Royal Academy of Sciences of Berlin. Trans- 

 lated and published in the Quarterly Journal of the Geological Society of London, Vol. ii, part 2, page 20, with two 

 plates. This memoir should have been cited under Caryocrwms ornatus. 



t The Cystidese were described by Von Buch as being entirely destitute of arms, and in this respect they would 

 show an important deviation from the CrinoideJB. M. Volborth, on the other hand, maintains that the Cystideae all 

 have arms, and that they are true Crinoideae. His argument is as follows : 



" All the Cystidese, like Crinoideae, were provided with articulated arms ; and this statement is not mere hypothesis, 

 " but the result of philosophical induction from distinct well grounded facts, determined by observation, from the 

 " presence of arms in some species, and the presence of tentacle furrows in others. The Cystideae are likewise true 

 " Crinoids. Either in the young state, or throughout life, they were attached by an articulated stalk, or by a pedicle, 

 " either to the bottom or to foreign bodies. They had articulated arms, which, as in Crinoideae, proceeded from the 



[Pal^eontology — Vol. ii.] 30 



