THE CRINOIDEA 



and, what is rather unusual, not meeting post. O in centre ; anus unknown ; 

 5 groups of short arms lie where the interoral sutures meet the RR, 

 which is not in the middle of any RR except ant. R (see Fig. LXIII. 2) ; 

 each arm-group appears to consist normally of 3 elements, 2 inner and 

 1 outer, all springing equally from the calyx ; stem with small axial canal. 

 Genus Zophocrinus, S. A. Miller (1891), Silurian, Indiana (Fig. LXIII.). 

 Theca pear-shaped ; Miller says there are 5 arm -plates in each group, and 



Fio. LXIII. 



Zophocrinus Iwwardi, from a specimen in the collection of Hon. F. Springer. 1, from 

 posterior, x f ; 2, oral surface, x ^' ; 3, dissection of plates. 



this may be so in some specimens ; these arm-plates may be compared 

 with the arms of Catillocrinidae, but whether they bore further Br is 

 uncertain. The tetramerism of this genus affects the cup only, and was pro- 

 duced by fusion, not by atrophy as was probably the case in Herpetocrinus. 

 FAMILY 8. HAPLOCRINIDAE. Monocyclica Inadunata, with 5 BB, 5 

 RR, of which 1. ant., r. post., and r. ant. are compound ; tegmen composed 

 solely of 5 0, one being pierced by a pore (? anus + hydropore) ; 5 arms, 

 unbranched and non-pinnulate, the food-grooves supposed to be subteg- 

 minal. Genus Haplocrinus^ Steininger (1837 ; Aplocrinus, d'Orb. ; see 

 W. & Sp., 1886), Devonian, Europe and N. America (Figs. XXXV. 

 and LXIV.) ; resembles the typi- 

 cal Heterocrinidae in its cup, 

 the Pisocrinidae in its arms, 

 and Allayecrinus in its tegmen. 

 The pore in post. O was dis- 

 cussed on p. 126. FAMILY 9. 

 ALLAGECRINIDAE. Monocyclica 

 Inadunata, with 5 BB, 5 RR all 

 simple, but of unequal and vari- 

 able size, the larger ones often 

 bearing 2 arms, while some arms 



may occasionally be absent or diminished in size ; tegmen composed in 

 the young of 5 0, one pierced by a pore (? anus + hydropore) ; 5 arms un- 

 branched and non-pinnulate, the food -grooves supposed to be subtegminal. 

 Genus Allagecrinus, Etheridge & Carpenter (1881, restricted by W. & Sp., 

 1886), Lower Carboniferous, N. America, Upper Carboniferous, Scotland, 

 resembles Haplocrinus in its tegmen, while the duplication of arms is 



RR 



Fio. LXIV. 

 Dissection of cup of Haplocrinus. R' = radianal. 



