THE CRINOIDEA 



Fio. XCV. 



Analysis of cup of Achradocrinus 

 veutrosus. 



Gasterocoma, but ant. R small, without facet ; r. ant. R with 2 facets. Scolio- 

 crinus, Jaekel (1895), Devonian, Eifel ; still more bilateral, in that ant. 



and 1. ant. RR are larger than the rest, and 

 alone bear arms ; anus below r. post. R, 

 and x between post. B and r. post. B. 

 Achradocrinus, Schultze (1867), Devonian, 

 Eifel (Fig. XCV.) ; x below anus, and 

 resting on post B ; IBB 5 ; stem round, 

 with single canal. Hypocrinus, Beyrich 

 (1864), Carboniferous, Timor ; differs from 

 Achradocrinus in having IBB fused to 3 ; referred by most authors to 

 Cystidea Aporita. 



SUB-ORDER 2. Dendrocrinoidea. Dicyclica Inadunata with a thin 

 flexible tegmen, or with the ventral surface almost entirely occupied by 

 a large anal tube or ventral sac (the latter name being needed if the 

 extension contained more than the mere rectum) ; orals inconspicuous or 

 entirely atrophied in the adult ; no madreporite ; radial facet often wide, 

 so that the distinctness of arms from dorsal cup is not maintained ; arms 

 dichotomous, the dichotomy often irregular, leading up to a pinnulate 

 stage. 



Whereas the genera of the Cyathocrinoidea all have the arms either 

 quite distinct from each other above the level of the patina, or at least 

 not united by supplementary plates, the Dendrocrinoidea gradually attain 

 a stage of development in which the arms are thus partially united. 

 Below this stage we may draw a somewhat arbitrary line, separating the 

 former as a grade, Distincta, from the latter grade Articulata. This 

 line happens to correspond with the break between Palaeozoic and 

 Mesozoic time. We deal first with the Dendrocrinoidea Distincta. 

 FAMILY 1. DENDROCRINIDAE. Dendrocrinoidea with regularly dich- 

 otomous, non-pinnulate arms, with anal x, and large RA in its 



Honoerinns. Fio. XCVI. Thenarocrinu*. 



Dendrocrinidae. Analyses of cups. 



primitive position as inferradial (Fig. XCVI.); stem quinquepartite. 

 Genera Merocrinus, Walcott (1883), Ordovician, N. America and England, 

 resembles locrinus (p. 145) in all but the presence of IBB ; anal tube sup- 

 ported by the left shoulder of r. post Rs. Ottawacrinus, W. R. Billing* 



