230 



ECHINODEEMATA— PELMATOZOA 



PHYLUM IV 



the basals being separated by distinct sutures ; columnals very short, but 

 little longer than broad, more or less barrel or bead shaped ; radials (and 

 arms) invariably five. Eecent ; trojjical Atlantic and East Indies. 



Bathycrinus Wyv. Thomson [Illycrinus Danielssen and Koren ; Pterocrmus 

 Wyv. Thomson). Essentially similar to Rhizocrinus, but with ten arms, each 

 post-radial series dividing on the second ossicle ; basals usually much reduced, 

 forming a narrow ring beneath the much larger radials. Eecent, chiefly occur- 

 ring at great depths, cosmopolitan. 



Monachocrinus A. H. Clark. Similar to the preceding, but with the basals 

 separated by distinct sutures, and usually nearly or quite as large as the 

 radials, sometimes larger. Lower Muschelkalk ; near Rovegliana. Eecent ; 

 East Indies, Bay of Bengal, east Atlantic. 



Family 2. Phrynocrinidae A. H. Clark. 



Similar in general to the Bourgueticrinidae, but with the stem attached to a heavy 

 terminal stem-plate (dorsocentral) as in the Apiocrinidae. Eecent. 



Here are placed the two genera Naumachocrinus and Phrynocrinus Clark, 

 occurring at depths of from 500 to 650 fathoms in the Pacific Ocean. The 

 former of these has a calyx superficially resembling that of Bemocrinus, but 

 composed of very small basals and much elongated radials. 



Family 3. Apiocrinidae d'Orbigny. 



Column without cirri ; enlarged distally and attached to a heavy terminal plate, 

 or fixed root ; composed of short, discoidal columnals having their articular faces 

 marked with radiating striae without fulcral ridge ; those next below the calyx often 

 increasing greatly in width, forming a proximcd enlargement continuous with the sides 



of the calyx. In the more highly 

 specialised types the proximal colum- 

 nals may become pentagonal or 

 stellate, and may bear rudimentary 

 cirri. Calyx variable, composed of 

 heavy plates. Infr aba sals greatly 

 reduced, modified or fused with the 

 proximal cokimnal ; visible rarely 

 tvitliin the basal ring (crypfodicyclic). 

 Lower brachials more or less incor- 

 porated in the calyx by lateral union, 

 or by a few interbrachial plates. 

 Primibrachs two ; arms branching 

 regularly, usually more than once. 

 Jura, Cretaceous and Eecent. 



Apiocrinus Miller (Figs. 334- 

 336). Plates of calyx greatly 

 thickened, especially at the distal 

 border of the radials, where the typical muscular articulation is modified 

 by an enormous enlargement of the dorsal ligamental fossa, consequent upon 

 such thickening ; this expansion aff'ects in addition to the calyx, a series of 

 the upper columnals, and of the lower brachials. Calyx in typical foi-ms 



IJan- 



Firi. 334. 



Apincnmift 'jiarkivftnni Sehlothcim. Great Oolite 

 ville, Calvados. <(, Calyx and upper sttiiii-joiuts, viewed J'rorn 

 the side ; '-, Ventral aspect ; c, Articular surface of one of the 

 stem-joints (natural size). 



