376 DR F. A. BATHER. 



layer therefore it would be no evidence. This view would he proved by finding an 

 impression of the inner face of the plates showing the same ridging. 



§ 55. The Mesostereom, according to Barrande, is laminate and not canaliculate, 

 although he mentions doubtful traces of some pores on the surface. These are repre- 

 sented in his pi. 26, f 11, as very minute diplopores, but the definiteness of the appear- 

 ance is probably due to the draughtsman. I have been unable to find any trace of 

 undoubted pores in the available material of any species. In a few specimens, as seen 

 under favourable illumination with a low-power lens, the ridges left on the imprints in 

 the position of the sutures between the plates have a somewhat wavy or notched appear- 

 ance ; and one is tempted to infer that the sutures may have been crenelate, or that the 

 plates may have been united by strands of mesostroma which left their trace in the 

 fascicular arrangement of the stereom at the borders of the plates (PI. II. fig. 23). But 

 on applying a higher power, this appearance is generally resolved into irregular grains 

 of sand, so that clear evidence is still wanting. 



§ 56. The Hypostereom (" epiderme interne ") according to Barrande is represented 

 by a thin, reddish layer, on which are a very few scattered tubercles. These might be 

 regarded as the ends of small canals, but Barrande was undoubtedly correct in declin- 

 ing to attribute any such nature to them. The reddish layer does not, of course, imply 

 the previous existence of any hypostereom, though it may in a certain sense represent 

 the hypostroma among other organic tissues. 



§ 57. Modifications of Thecal Plates. — In addition to the umbonate, ridged plates 

 already discussed, we have to consider three real or supposed modifications. (1) Br 

 Jaekel (1901, p. 673) mentions "a folded plate at a lower corner, which corresponds 

 to the thick corner plate of Ceratocystis (erroneously taken by Haeckel for a valvular 

 anal pyramid)." If Dr Jaekel is referring to Prof. Haeckel's remarks on p. 56 of 

 his " Amphorideen und Cystoideen," I am not certain that both authors allude to the 

 same thing. The only structure that seems to correspond with Dr Jaekel's description 

 is a hexagonal or pentagonal ridged plate, 9 "3 ram. in greatest length, represented in 

 Barrande, pi. 26, f. 2, at apparently the lower corner of the adbrachial side of the 

 theca. A plate of similar appearance, but only 5 mm. long, is associated with the 

 original of Barrande, pi. 26, f. 6, at the lower corner of the antibrachial side of the 

 theca, but is not distinguished in the figure. This latter plate, though somewhat Hke 

 the umbonate plates, is more than twice their diameter and apparently bears concentric, 

 coarse striae between the ridges (PI. I. fig. 5, marked x). In Barrande's fig. 2 it is 

 relatively larger. In both cases it lies above the plates of the theca and has no very 

 obvious connection with them. No such plate is associated with any other specimen 

 known to me, of any species of Dendrocystis. Therefore I do not regard this plate as 

 having anything to do with the two individuals near which it is found, or even as 

 belonging to any Dendrocystis. 



§ 58. Whether this is the structure Dr Jaekel had in mind is another matter. 

 There is actually in Dendrocystis, or at least in some species or in some individuals, a 



