438 



PELMATOZOA. 



Division B. Neocrinoidea. 



This division of the Crinoidea corresponds with the Articulata of 

 Miiller (with the addition of the genera Marsufiites and Uintacrinus), 

 together with the Costata of the same author. As defined by Dr 

 P. Herbert Carpenter, the forms included in the Neocrinoidea possess 

 a relatively minute, usually symmetrical, regularly pentamerous calyx, 

 the arms being in general greatly developed. There are, as a rule, 

 five equal and similar basals, and five also equal and similar radials. 

 Underbasals are rarely present (Encrinus, Extracrinus, and Marsu- 

 pites). Interradials are rarely developed, and, when present, no 

 special " anal " interradius (except in Thaumato- 

 crinus alone) is recognisable. The higher radials 

 do not enter largely into the composition of the 

 calyx, and are usually more or less movable, 

 being generally united to the succeeding plates 

 by a muscular articulation. The ventral surface 

 of the calyx is not concealed by an external 

 canopy or vault of calcareous plates, but the 

 aperture of the mouth, with the ambulacral 

 grooves converging to it, is exposed to view. 

 The ambulacral grooves may be more or less 

 roofed in by calcareous plates, and " oral " plates, 

 when present, " may be limited to larval exist- 

 ence, or remain through life partially covering 

 the peristome, but capable of being separated 

 so as to open the mouth to the exterior" (P. 

 H. Carpenter). All the Neocrinoids are Second- 

 ary, Tertiary, or Recent, no Palaeozoic represent- 

 atives of the division being at present known. 



Family i . Encrinidoe. — In this family the calyx 

 is shallow and basin-shaped, with a "dicyclic" 

 basis. There are five underbasals, which are 

 of very small size, and are concealed by the 

 uppermost joint of the column. These are 

 succeeded by five large basals, followed in turn 

 Fig 12 —Encrinns by ^ ve ra -dials, the whole of these plates being 

 uuiformis. Muschd- firmly united by suture. The primary radials are 

 shows th e e anfcuiaulig followed by two others, the second of which is axil- 

 coiumn-jofnts . 11 " ° f the lary and bears two arms, which sometimes fork 

 again, so that there are ten, or, rarely, twenty divi- 

 sions in all. The arms (fig. 312) are often biserial, are abundantly 

 furnished with pinnules, and form by their apposition a kind of 

 pyramid. The upper column-joints (fig. 312) are generally alter- 

 nately large and small. The joint-surfaces are furnished with 



