238 



ECHINODEEMATA— PELMATOZOA 



PHYLUM IV 



Fig. 341. 

 PlicatocHmis hexagonus Müust. 



first brachial, never on the second. If the arms are undivided the pinnules are 

 usually excessivehj long and reach to the arm Ups ; hut the length of the pinnules 

 decreases in proportion to the number of arm divisions ; pinnulars sometimes tending 

 to fuse into a solid piece. Column as in the Apiocrinidae, but never with a proximal 

 enlargement. 



Plicatocrinus von Münster (Fig. 341). Eadials comparatively thin, their 

 articular facets crescent-shaped ; the outer faces longitudinally folded into 

 a median ridge. Arms ten, dividing on the first brachial ; composed of 

 wedge-shaped ossicles united by perforate muscular articulation. Pinnules 

 composed of a single piece, except the proximal ones, which consist of three 

 pieces ; they are angular or keel-shaped along the dorsal side, and deeply 



furrowed on the ventral. Teg- 

 men unknown. Upper Jura; a 

 rare form, found in the Fran- 

 conian and Swabian Alb. 



Hijocrinus Wyv. Thomson 



(Fig. 342). Three basals ; five 



Upper arms, bearing extremely long 



Jura ; Streitberg, Franconia. a, Calyx with ■niTinnlp«! wViipVi rpnpVi fn fliP 



radials and undivided base ; h, c, Dorsal and PUmUieS wnicn reacn tO tne 



lateral aspects of same (slightly enlarged) ; arm tips ; brachials unitcd in 

 d-f, First brachial, seen from the inside, out- . -, - , ■, ^n 



side, and from below respectively. Syzygial grOUpS Ol three. i eg- 



men composed of five large 

 orals, surrounded by heavily 

 plated perisome. Recent ; 

 Antarctic Seas. 



Gephyrocrinus Koehler and 

 Bather. Similar to Hyocrinus, 

 but brachials united in syzy- 

 gial groups of two; proximal 

 portion of column pentagonal. 

 Recent ; Canaries and Madeira. 



Thalassocrinus A. H. Clark. 

 Similar to Gephyrocrinus, but 



Hyocrinus Ijethellianus Wyv. Thomson. Recent; Atlantic prOXimal portiou of Column 



Ocean. A, Individual twice the natural size. B, Tegmen several hexagOnal. Rcceut " Philip- 



tiraes enlarged ; am, Ambulacral furrows of the arms ; c. Dorsal . " * •' " 



canals ; an, Anus ; m, Mouth ; o, Orals (after Wyville Thomson) ; pines. 



s,Coveringplatesof ambulacral grooves. PtilocrinUS A. H. Clark. 



Five arms, unbranched ; each brachial, except the most proximal, bears a 

 pinnule ; syzygies very infrequent ; pinnules not especially long. Recent ; 

 Antarctic Seas and west coast of America to British Columbia. 



Calamocrinus A. Ag. Five brachials ; the arms brauch several times. 

 Recent ; Galapagos Islands and Central America. 



Fig. 342. 



Family 6. Saccocomidae d'Orbigny. 



Calyx small, hemispherical, non-pedunculate, composed almost exclusively of 

 five radials, which are very thin, elevated into prominent ridges along the median 

 line, and enclose an extremely small basal plate. Arms 5x2, slender, widely 

 separated, and giving off alternately towards the extremities simple incurving 

 l)ranches. Arm-plates cylindrical ; each side of the ambulacral furrow lined with 



