III. Asteroidea. 1 1 



generally accompanied by the presence of an ambulacral skeleton, and recalls the 

 condition of the Jurassic A. costata. It is much exaggerated in Encrinus and in 

 some species of Apiocrinus. 



Wagner describes a specimen of Encrinus Wagneri which confirms the views of 

 v. Koenen and Giirich respecting the ventral covering of the calyx in this genus 

 [see Bericht for 1887 Ech. p 6]. It was a plated perisome extending from the 

 upper edge of the first radials at least as far as the third arm-joint, and the 

 plating was more compact in the centre than in the peripheral parts which were 

 fairly moveable. 



Eck notices an abnormal form of Sphaerocrinus. The pentagon of under-basals 

 is truncated at one angle, to make room for a small 6 th basal. But there are 

 only 5 radials, one of which rests on the additional basal, and has its lower 

 margin concave instead of convex. 



Barrande describes 3 types of stem as occurring among the Cystideans. 

 Echinoencrinites, Glyptosphaerites , etc. have an ordinary crinoidal stem composed 

 of simple joints. In Echinosphaerites infaustus (Arachnocystites, Neumayr) and a 

 few other genera the stem is composed of 5 or 6 longitudinal rows of alternating 

 plates, and its general structure shows a striking analogy with that of the arms. 

 In Dendrocystites Sedgivicki and in certain other types the lower part of the stem 

 is of the ordinary crinoidal character; but the upper part gradually widens 

 towards the body and is enclosed in nearly horizontal rows of numerous small 

 and irregular plates. Lichenoides prisons has no stem nor any indication of attach- 

 ment. - - In Aristocystites and some other genera the test proper is enclosed in a 

 smooth calcareous film, the external epidermis, which covers both the ornamen- 

 tation and the openings of the hydrospires; and there is a similar internal epi- 

 dermis, bearing tubercles which are often perforate. Besides mouth, anus, and 

 genital pore, Aristocystites has a 4 th opening of sublinear shape, situated close 

 to the mouth and of unknown function. Five genera are described with 3 orifices, 

 five with 2 and twelve with 1 only ; while in six others no orifices have yet been 

 discovered. Dendrocystites has a proboscis like that of the Poteriocrinidae ; 

 but Neumayr regards this structure as rather comparable to the arms of Arachno- 

 cystites. - - Neumayr further points out that the hydrophores palmes de- 

 scribed by Barrande in Aristocystites and Craterina and compared by him to the 

 hydrospires of other Pelmatozoa are the remains of subtegmiual ambulacra. 



III. Asteroidea. 



See also Barrois, supra, p 2, Bury, supra, p 3, Neumayr, supra, p 5, Semon, 

 supra, p 3. 



Cuenot( 1 ) has studied the minute anatomy of the Asterids. Most of the connec- 

 tive tissues are derived from embryonic cells with granular protoplasm and 

 large rounded nuclei, each containing arefractilenucleolus. Cells of this class, either 

 spherical or stellate, are abundant in the integument. Others become modified 

 into long fibres, especially in the tentacles, papulae, and other organs which 

 undergo considerable changes of form. A third type is that of more delicate fibres 

 with fusiform nuclei which occur in the stems of pedicellariae, the mesentery, and 

 other organs where strength is needed. The ground substance of all the connec- 

 tive tissue is a compact and elastic feltwork of fibrils containing scattered nuclei. 

 In the skeletal tissue this forms irregular areolae and contains numerous stellate 

 embryonic cells. The muscular fibres are unstriated, and in no way related 

 to ectoderm cells, resulting directly from the transformation of the embryonic 

 cells. They contract readily on application of a simple stimulus. The ecto- 



