54 Dr. F. A. Bather — Eocystis. 



2. The two specimens labelled " Plates showing Marginal Pores " 

 are in the form of impressions. One of thera (E 7608) looks strangely 

 like one-half of the pectinirhomb of a Glyptocystid ; but the 

 resemblance disappears when one examines a wax squeeze of it. 

 I believe this specimen to be the impression of the sutural margin of 

 a plate 3-8 mm. long, about -6 mm. thick at the corners, and 1 mm. 

 thick in the middle of the side ; the sutural surface is covered witli 

 slightly irregular vertical ridges, about five to the millimetre, and 

 these may have been crenelations fitting into corresponding notches 

 in the adjacent plate. These ridges pass right down to the concavely 

 curved margin, which I take to be on the inner side of the plate ; 

 but on the outer convexly curved, or, rather, gabled, side they 

 stop short, so that the suture, if sutxire it be, was grooved. In the 

 middle of the side, however, forming, as it were, the rooftree of the 

 gable, is a rather large prominent vertical ridge, probably continuous 

 with an axial fold or ridge. Clearly this impression has nothing to 

 do with the stellate plates, and there is no adequate reason for 

 supposing that the plate which made it belonged to the same 

 organism. 



The other impression, Gr. F. M. c (Fig. 8), appears to have been 

 formed by the folded edge of a plate which had fallen obliquely into 

 the mud. The space formerly occupied by the plate, having been 

 subject to less compression, is thicker than usual. The walls of the 

 cavity are marked by about seven ridges, varying in distinctness, and 

 passing across its thickness. A squeeze of the cavity indicates that 

 these ridges correspond to indentations or scoUopings in the margin 

 pf the plate, lying between its folds. If several plates of this shape 

 lay next one another in the thecal wall there would be the appearance 

 of pores between them. It is quite possible that this is one of the 

 stellate plates, and that others of them had a similar margin. 



3. The impressions referred to Columnals are in the main of two 

 kinds, long and short. The long ones vary in length from 1 to 3 mm., 

 with a diameter from i to i their length. The diameter appears to 

 be least about the middle ; in other words the ossicles were slightlj- 

 dice-box shaped (Fig. 15). At each end was a conical excavation 

 penetrating to a depth about equal to the width of the respective 

 columnals. In the impression this appears as a' deltoid patch of 

 matrix, and is sometimes so pronounced as to give the impression 

 a bifurcate appearance, G. F. M. ff (Fig. 14). In a few cases this may 

 be seen at both ends, but more often the matrix has been split 

 obliquely to the long axis of the columnal, so that in a single half of 

 the impression this cone appears only at one end. The sides of the 

 columnals seem to have been marked with irregular vertical striae, 

 perhaps due to the original fascicular structure of the stereom 

 (Fig. 10, b). 



The short columnals leave an impression that approaches a square, 

 but has the two sides slightly inflected. E 7607 has a length of 

 about -75 mm. and shows no cone at the ends. One of Dr. Matthew's 

 specimens (d, Fig. 13) is about -25 mm. long, and has a flattened cone 

 at each end. 



There is no direct evidence that these columnals belonged to the 



