CAMBRIAN 237 



cut in much the same direction. It is much older, however, for in the Antarctic speci- 

 men the pores of the inner wall are nearly as large as the loculi (between the septa). 

 This illustrates a feature of the Archccocyathince — the constancy in the size of the 

 mural pores. Of the latter there are nine to the millimetre, which is a usual number. 



Another interesting feature is that the walls here are waved, as if the structure 

 arose through the adding of one rounded cell at the side of another. This is lost 

 in almost all mature forms (except perhaps A. tvirrialpensis, vide photo 44), and 

 perhaps hidicates the origin of the Archavcyathus in a foraminiferal-like organism of 

 the Textularian type. This minute specimen bears out my statement that the inner 

 wall and septa are present in the earliest stages, which do not consist of simple 

 stalked beakers, as was suggested by Von Toll. ( Vide pp. 167-8 Memoir.) 



Plate LXXVII. Fig. 1. This is a vertical section through a small cup of a 

 much more irregular nature than that represented in Slide (2) 68, j^hoto 1. The 

 thickened basal portion and thicker outer wall are quite usual, and have been 

 noticed in many young forms. The inner wall and septa are not clearly differ- 

 entiated. Probably it is a young Protopharetra in which the intervallum is occupied 

 by irregular meshwork. If so, it is of interest as tending to confute Bornemann's 

 argument that the Protopharetrce are merely vegetative or rooting stages of the 

 more regular forms. {See p. 113 Memoir.) 



Plate LXXVII. Fig. 2. A fragment of a regular Arclueocyathus showing three 

 septa cut transversely. [See also Slide 118, photo 34 (12) next following.) 



Plate LXXVII. Fig. 3. Fragment of three parallel septa are here preserved. 

 They show that regular Archceocyathince were present. They recall the close-set 

 regular septa of certain of the Siberian species, such as A. ijizhii of Von Toll. [See 

 Fig. 26, No. 3 in Memoir.) 



Plate LXXVII. Fig. 4. Five septa of an anastomosing species like A. pirofundus. 

 Notice the solid dark core and irregular powdery zones in the outer portion of the 

 septa. 



The septa are somewhat less than a millimetre apart. There is some appearance 

 of an outer wall on the right. This photo should be compared with that given in 

 the Memoir, Plate IX., photo 53, of an allied species, A. dissepimentalis. 



Plate LXXVII. Fig. 5. A fragment of an irregular Arclueocyathus, possibly 

 akin to A. profundus, showing anastomosing septa. 



The differentiation of the septal laminae into light and dark zones is remarkable, 

 for here the inner band is the lighter and the outer more dense, whereas the opposite 

 is the usual apjiearance. It is possible that the feature (in both cases) is purely 

 secondary. 



Slide 110 shows a similar fragment. Three septa and a dissepiment of the 

 same form as in the photo above, but the central laminse are the denser here. 



Plate LXXVII. Fig. 6. Three septa of a regular Archceocyathus with dis- 

 sepiments. These are much slighter structures than usual, and belong to a different 



2 H 



