544 Prodromus of the 



versely semicircular, thin, minutely longitudinally folded, 

 the concave side of each one facing one of the flanks of 

 the quadrate camera ; the edge of each limb of "the semi- 

 circle two or three times deeply folded lengthwise ; the 

 breadth of each muscle rests against the middle of each 

 flank of the camera ; just above the base of the pedicel 

 each muscle is nearly as broad as the corresponding flank 

 of the camera, but at the base the muscle expands very 

 little, whilst the camera suddenly widens to a far greater 

 extent ; and in the opposite direction, toward the urn, the 

 muscle retaining the same breadth, the camera gradually 

 broadens, until each flank is at least three times as broad 

 as the muscle; and finally, when the muscle rather suddenly 

 narrows, by one half, just before it enters the proximal end 

 of a partition, the disproportion is still greater; radially 

 the muscles occupy about one half the thickness of the 

 gclatiniform layer : the principal muscles of the oral side 

 of the urn narrow-ligulate, thin ; each one extends to the 

 base of a tentacular tuft, a little to one side of the middle 

 line of an arm, and next the marginal sinus opposite a 

 corner of the mouth ; the marginal muscle very wide, 

 nearly as broad as the radial diameter of a group of tenta- 

 cles ; it is imbedded in the middle of a considerable thick- 

 ening of the musculo-gelatiniform layer, and is quite thick 

 itself, but thins out on each edge, one of which borders 

 close on the distal base of the pistilliform tentacles and 

 the anchors, whilst the other terminates with the musculo- 

 gelatiniform layer close to the edge of the aboral side : 

 gclatiniform layer almost imperceptible in the aboral side, 

 except at a short distance from its junction with the pedi- 

 cel, where it gradually thickens and merges into that of the 

 latter ; in the pedicel it is very thick, being in this respect 

 about twice the basal diameter of the largest tentacles ; in 

 the base of the pedicel it grows thinner, and at the under 

 side of the disc it is less than one quarter of its greatest 



