1886.] NATURAL SCIENCES OP PHILADELPHIA. 81 



axial canals, tlie inner and larger ones are probably ambulacral 

 openings. 



The arms of the Gasterocomidse have similar axial canals as 

 those of the Gupressocrinidse^ but these face outward, while the 

 others are directed upward. This is readily explained b}' the 

 condition of their articular facets, which are lateral, horseshoe- 

 shaped, and do not extend over the whole width of the plates. 

 The articular facets of the radials throughout this family, 

 instead of bending over to the ventral side, stand erect as in 

 Platycrinus, and their outer ends support the interradials in a 

 similar manner as in that genus. In accordance with this struc- 

 ture, it is evident that, if the anal opening was to occupy a posi- 

 tion corresponding to that of Symbathocrinus and Cupressocrinus, 

 it had to be located, as it is throughout this group, dorsally 

 between the upper portions of the radials, which resemble struc- 

 turally, if not quite functionally, the extensions of the muscle- 

 plates in the other groups. The radials of the Gasterocomidse 

 have limb-like extensions, they are simply notched for the ambu- 

 lacral canal, and their axial opening penetrates the median por- 

 tions of the plates. 



The Larviforniia agree with the Blastoids as to certain condi- 

 tions of their arm structure (see our notes on Gupressocrinus) , 

 and probably possessed hydrospires and hydrospire pores to 

 connect with the ambulacra ; Gupressocrinus even had similar 

 pinnules. The arms are simple throughout, but some of the 

 radials, exceptionally, support two arms. The arms were united 

 with the radials by strong muscles; but the arm-plates among 

 each other, so far as known, were suturally connected and moved 

 in a body. 



We give the following definitions of the four families : 



A. Haplocrinid^. Dorsal cup small, composed of basals and 

 radials ; covered ventrally by five large single interradial plates, 

 which form a pyramid. These plates are supported upon the 

 outer ends of two adjoining radials, and are united with one 

 another, leaving only a small ambulacral opening. There is no 

 anal plate; the anal aperture, so far as known, penetrates the 

 upper part of one of the interradials. Column with small 

 central canal. 



B. Symbathocrinid^. Dorsal cup small ; composed of basals 

 and radials only. The latter are provided with large muscle- 



