150 TERTIARY INSECTS OF NORTH AMERICA. 



the posterior euds showing like faint dots through the white covering. Those of the 

 margiDal row lie flat ou the attached surface ; the others gradually diverge outwardly, 

 so that the central ones are at right angles with said object. Beneath this vaulted 

 layer the rest lie on a plane with the leaf, those touching it in concentric rows, the 

 rest packed in irregularly.' 



In the fossil ootheca the mass is much larger and more elongated, and 

 possesses besides one characteristic in which it differs strikingly from that 

 of Corydahis (and on which account particularly I have used a new 

 generic appellation), viz, the division of its mass into two longitudinal 

 and equal halves by an albuminous wall, or rather by double albuminous 

 walls, which may be parted above, leaving as the only connection between 

 the two halves their common albuminous floor. There are indeed a few 

 specimens which show no sign of this division, Ijut a median furrow, or a 

 deeper and more complete separation of the two halves, is so prevalent that 

 this seems to be the only explanation te be offered for its appearance. 

 Their absence in the few specimens is probably due to defect of preserva- 

 tion. The common albuminous floor and the upper and outer albuminous 

 coating are of remarkable thickness, varying from one to three milli- 

 meters ; but the coating attenuates to a mere lamella as it passes down the 

 median furrow, so that when the mass remained quiet in the position in 

 which it was laid, the lateral halves pressing closely against each other, the 

 combined thickness of the two albuminous walls would together no more 

 than equal the ordinary thickness of the albuminous partition between any 

 two contiguous eggs. That such a partition existed even in those which 

 do not now show it seems probable from the regularity of the furrow in 

 every instance of its occurrence and by its prevalence ; some specimens 

 merely show a sharp groove along the middle, the halves remaining in 

 complete juxtaposition;^ others again are so completely separated as to be 

 curled over and meet beneath (Figs. 19, 23). 



This, together with the fact that the egg-mass is otherwise extremely 

 regular (showing only so little plasticity as to allow one broad side to be 

 straight, while the opposite is a little convex) and never exhibits the slightest 

 tendency to coil longitudinally, leads me to believe that the egg-masses 

 were laid in the water of shallow basins, upon the muddy floors, which 



'Proo. Am. Assoc. Ad. Sci., vol. 25, pp. 277-278. 



'These specimens are some from which weathering has removed their outer albuminous coating; 

 perhaps, if this had remained, the furrow would have been concealed by the complete union of the 

 attingeut albuminous walls. 



