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. 



Fig. 20. — Hexarhizites insignis. a, a it mouth seam (a 2 , remains of mouth opening ?) ; b. lateral branch of the mouth 

 seam ; Cj-Ca, bifurcation points of the perradial seam at the base of the 6 oral arms ; d,, (l l2 , the limbs of this bifurcation, 

 by which the oral disk falls into G 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 subgcnital operculum {g) is arched, while a radial furrow (/) can be seen in the 

 middle of their basal periphery, i.ringcanal; k, perradial canal ; I, interradial canal. The marginal bodies (m) are shown 

 at the end of this radial canal. The rim is split up into 144 marginal lobes. 



When we compare the mid -field of Hexarhizites insignis with that of Rhizostomites 

 admirandu8, 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 S alternating triangles of the oral disk of Ehizostoinites. 



Dr. Amnion studied the specimen described by Dr. Haeckel, and found 



the oral suberenital lids referred to under Rhizostomites admirandus and 



