E. Billings on the structure of the Crinoidea, ete. 81 
the side opposite, or toward the central axis of the visceral 
cavity, is more or less deeply folded longitudinally. There are 
two of these to each ambulacrum, attached along the two lines 
of pores. There appears to be a fissure extending nearly the 
whole length in the direction of the dotted line /. One edge 
pra ae Fi ee aa) , 
7 
Fig. 12. aus A he Bi soa of the hydrospires of a Pentremite,—a, the in- 
b, er, or side attached to the shell; f, the fissure. 
i f P. God 
. 
f ; ne 
two branches of one of the radial plate 15. Sum mit of fo! uciia —t, 
we soteie side; g, ambulacral grooves joaphadl from Dr. Shumard, Dae with 
fi the ovarian pores added), 
4 of this fissure, is attached to the lancet plate, along one side 
of the line of. pores ; the other to the shell, on the other side 
ra 
} 
: 
_ pairs, each pair communicatin with the exterior through a 
4 single apltanll The arrangement of the folds varies according 
to the species. In P. Godoni there are five folds, the outer 
sides of which are close up to the inner side of tho lancet 
_ plate, fig. 13. In a specimen of P. obesus Lyon, nearly two 
inches in diameter at the mid-height, the byrospiren extend 
_ Am. Jour. Sc1.—Seconp Seriss, Vou, XLVIIL No. 142.—Jur 
6 
