JURASSIC. 87 
without a sharp boundary into the genital zone, in which lie the six genital organs. 
The genital zone sinks gradually toward the exterior and is separated from the 
smooth zone by a circular furrow which is sometimes sharp and sometimes obscure. 
The latter (smooth zone) lies a little deeper and represents a slightly elevated plateau. 
It declines externally quite suddenly and steeply into the muscle zone or marginal 
zone, which lies much deeper, and, like a moat, as it were, divides the entire inner 
convex portion of the impression from the surrounding, more elevated portion of the 
shaly slab. 
Fia. 20.—Hexarhizites insignis. a, a, mouth seam (a2, remains of mouth opening?); b, lateral branch of the mouth 
seam; ¢,-cg, bifurcation points of the perradial seam at the base of the 6 oral arms; d), djy, the limbs of this bifurcation, 
by which the oral disk falls into 6 pairs of three-cornered areas. The smaller perradial fields are hatched; the larger 
(alternating with them) interradial fields are white. In the peripheral portions of the latter the triangular genital pouches 
are visible, over whose inner entrance a subgenital operculum (g) is arched, while a radial furrow (7) can be seen in the 
middle of their basal periphery. i, ring canal; k, perradial canal; J, interradial canal. The marginal bodies (m) are shown 
at the end of this radiai canal. The rim is split up into 144 marginal lobes. 
When we compare the mid-field of Hexarhizites insignis with that of Rhizostomites 
admirandus, we are convinced that the sharp projecting outline of the mid-field in 
both impressions must have the same significance. The 12 triangular areas of 
Hexarhizites, alternating in pairs, correspond in configuration and position completely 
with the 8 alternating triangles of the oral disk of Rhizostomites. 
Dr. Ammon studied the specimen described by Dr. Haeckel, and found 
the oral subgenital lids referred to under Rhizostomites admirandus and 
