154 



CRINOIDEA 



Evidence for its truly Monocyclic nature is wanting ; but in the 

 absence of proof to the contrary, it must be 

 left in this, apparently natural, position. The 

 stem is not unlike that of some Plicatocrinidae ; 

 the branching and syzygies of the unforked 

 arms remind one of the structure in the 

 arm-raini of Belemnocrinus and Saccocoma ; the 

 cup is not unlike that of Plicatocrinus Fraasi. 

 The only specimen at all complete is a male, 

 with testes probably mature and swelling out 

 in the proximal portions of the proximal 

 ramuli ; in these regions each ramular sup- 

 ports 2 or 3 square side-plates on either side, 

 and these support the covering-plates. The 

 orals could probably open to expose the 

 funnel - shaped gullet, which leads into a 

 narrow gut with single dextral coil ; glandular 

 ridges line the gullet and first part of the gut. 

 The intra-thecal connective tissue contains no 

 spicules. FAMILY 14. SACCOCOMIDAE. Mono- 

 cyclica Inadunata, in which 5 RR and a 

 minute centrale enclose a large spheroidal 

 thecal cavity : each R has a prominent median 

 ridge ending in a narrow facet, which sup- 

 ports a thin arm, forking on IBr., ; beginning 

 at about IIBr 15 , each ramus gives off from 

 every 3rd Br unbranched alternating ramuli 

 arranged as in Hyocrinus ; the rami and 

 ramuli are usually found rolled up in their 

 distal portions ; Br cylindrical, elongate ; 

 lax and the more proximal IlBr may bear 

 lateral, paired, wing-like expansions, which 

 in the more distal Br and the rarnulars are 

 always represented by delicate trellised pro- 

 cesses, with thicker upper and under mar- 

 gins, which it is conjectured supported a 

 continuous membrane ; no stem ; all skeletal 

 elements very thin and coarsely reticulate. 

 Genus Saccocoma, L. Agassiz (1834 ; syn. 

 Euryale, Konig), Solenhofen Lithographic 

 Stone, Upper Jura (Fig. LXVIIL). Jaekel, 

 who has admirably elucidated the structure 



lianus. (From an( j amn iti e s of this wonderfully specialised 



Challenger Narra- J 



tive, x ?.) cnnoid (1893), considers that the arms were 



swimming-organs, the food-groove, ambulacral, 

 and genital systems being atrophied at their 

 distal ends, and that the animal was pelagic, 



floating in enormous swarms in the peaceful lagoons of Eichstiidt and 



Solenhofen. 



FIG. LXV1I. 



Hyocrinus bethel- 



