432 PELMATOZOA. 



rocks ; and the genus Forbesiocrinus, with a similar geological range, 

 is principally distinguished from this by the more abundant develop- 

 ment of the interradial plates. 



Family 8. Haplocrinidce. — In this family the calyx is small and 

 spheroidal, and is composed of basals and radials, underbasals 

 being absent. The ventral surface of the calyx exhibits five large 

 " oral " plates, forming a low pyramid, which is excavated along the 

 sutures of the plates to receive the bases of the arms (fig. 305). 

 There is no definite anal plate, but the anal opening perforates one 

 of the oral plates, which is somewhat larger than its fellows. The 

 arms are poorly developed. The family, as defined by Wachsmuth 

 and Springer, includes only the two genera Haplocrinus (fig. 305) 

 and Allagecrinus, of which the former is mainly if not wholly De- 

 vonian in its range, while the latter is exclusively confined to the 



Fig. 2,0^.— Haplocrinus mespiltformis. The calyx viewed from below, from one side, 

 and from above, and enlarged. Devonian. 



Carboniferous rocks. Both genera comprise very small Crinoids, 

 which are in some respects simpler in their construction than the 

 normal members of the order, and may be considered as perma- 

 nently representing the larval condition of the Palseocrinoids. 

 Allagecrinus is remarkable for the inequality in the size of its 

 radials, some of which may be axillary and bear two arms. For 

 this reason it is regarded by some authors as the type of a distinct 

 family. 



Family 9. Symbathocrinidce. — In this family the calyx is small, 

 and is composed of basals and radials only. The central portion 

 of the ventral surface of the calyx exhibits a circle of oral plates. 

 The arms are uniserial, exceedingly long, and folded together. The 

 principal genera of this family are Symbathocrinus (Devonian and 

 Carboniferous), Pisocrinus (Silurian), and Triacrinus (Devonian and 

 Carboniferous). 



Family 10. Cupressocrinidaz. — In this family the large, basin-shaped 

 calyx is apparently of the "dicyclic" type, the underbasals being 

 anchylosed to form a solid disc, which some authors regard as 

 being an enlarged top stem-joint, in which case the calyx would 

 be " monocyclic." Upon this disc rest five basals, followed by 

 five radials, the upper edges of which are truncated and form a 



