habit of naming the most characteristic members of the 
group “Archaeocyathus,” but Gordon in 1920 (Trans. 
"Roy. Soc. Edinburgh) and Okulitch in 1937 (Journal of 
Palaeontology) have both pointed out that this is not 
permissible. Gordon held Archaeocyathus profundus, 
Billings (1865), to be the type species of Archaeocya- 
thus; but Okulitch shows clearly that Archaeocyathus 
atlanticus, Billings (1861), is actually the type species. 
The position now becomes rather complicated. Gordon, 
holding profundus to be the type species, says, "It is 
impossible to group the present forms known as 
Archaeocyathus under Billings? original (i.e. atlanticus) 
or amended (i.e. profundus) definition."  Gordon's 
reason for this is, we take it, the presence of dissepi- 
ments in 4. profundus. Gordon then proceeds to erect 
a new genus for the regular forms, which he calls 
Thalamocyathus, but he gives no genotype; the first 
species he mentions is tubavallum, Taylor, a very unlucky 
choice, because it is founded on a single abnormally 
preserved fragment and is about the only one’ of 
` Taylor's numerous species of which confirmation is 
lacking; besides this Taylor's two figures of tubavallum 
are mutually contradictory; his figure 28 shows the 
inner view of the inner wall with 2 or 3 rows of 
regular pore-pipes to the intersept, rather as in his 
description, whilst figure 29 shows an irregular wall, 
somewhat resembling retezona. The second species he 
mentions is trachealis, Taylor, a perfectly good and 
plentiful species, but not of the simple generic type we 
are considering, of which type it is a specialised 
development, which would now be put in a separate 
family. 
(Gordon's photograph of his fossil which he refers 
to A. tubavallum is very close to A. retezona (Taylor).) 
Okulitch (l.c.), rightly considering A. atlanticus as 
the genotype of Archaeocyathus, and dropping the genus 
Spirocyathus as invalid, because it was founded by 
Hinde (1889) on Archaeocyathus atlanticus, and is there- 
fore an exact synonym of Archaeocyathus, proposed a 
new genus Cambrocyathus “to include Archaeocyathus 
| profundus and its congeners.” ^ The question now arises 
as to the interpretation of “congeners,” which, by 
‘implication, Okulitch appears to take as including the 
regular Archaeos we are now discussing; he says also, 
` “Cambrocyathidae to be used instead of Archaeocya- 
thidae (as used by Hinde, Bornemann, Taylor, Vologdin, 
Bedford, and Okulitch).” This, however, is not, we 
"think, practicable, because Archaeocyathus | profundus 
(Billings, 1935), whatever it is, is not a member of the 
` group we are discussing; it is a very large form, more 
` * than a foot in length with a diameter of two to four 
‘inches; «the external surface has strong circular ridges, 
about 3 inch apart and 1 inch deep, and Billings’ figure 
shows synapticulae or dissepiments between the septa. 
its 
It is clear that Cambrocyathus (Okulitch) with 
` ‘genotype profundus (Billings) is not the type we are 
` now looking for; on the contrary it has some resemblance 
t 
| 
| 
71 
to Pycnoidocyathus, Taylor, but we have not sufficient 
data to relate it definitely to any group with which we 
are acquainted, 
The only other genotypes for consideration are the 
following :— 
Ethmophyllum whitneyi, Meek (1868). 
The genus, as originally described by Meek, has an 
outer wall “beautifully punctuate, the punctures being 
minute, of exactly uniform size, and arranged with 
mathematical regularity in quincunx, and so closely 
crowded that... ." Septa straight near outer wall, 
becoming regularly waved further in. ^ Two rows of 
alternating canals within each interseptal space at the 
inner wall. “These canals . . . do not pass directly 
through the inner wall, but are directed obliquely 
upward and inward, so that as seen in transverse sections 
. they present the appearance of a double row of 
vesicles cut across." , 
Meek says apparently two species. were present, the 
larger one, E. whitneyi, being the type. He makes no 
mention of the character of the inner wall and septa 
and leaves it to us to guess if he meant the generic 
description to apply. The smaller species “differs from 
the other in having its septa so strongly waved laterally 
as almost to divide the interseptal spaces into cells, 
nearly to the outer wall”; this he calls Ethmophyllum 
gracile. 
Meek gives no illustrations, and a few months later 
abandoned the genus in favor of Archaeocyathus. 
"Walcott resuscitated the genus in 1866 and gave it a 
much wider extension, to include whitneyi, minganense, 
profundum, rensselaericum, rarum. He also published 
several figures of whitneyi, some said to be from types. 
Three widely different Archaeos appear in these figures, 
and in none of them do the septa and inner wall cor- 
respond- with. Meek's description. d 
Hinde in 1889 (Q.J.G.S.) redefined the genus on the 
lines of Meek's original generic description. 
We must accept oblique canals opening inwards and 
upwards into the central cavity as an essential feature 
of the inner wall of Ethmophyllum; it cannot, therefore, 
serve as the type of the group under consideration. 
Archaeocyathellus ? rensselaericus, Ford, 1873. . 
This appears to be the first tentative suggestion of a 
generic name for what appears to be a small regular 
Archaeo. Ford, however, does not seem to have 
confirmed the name; he said, “Should a further study 
of it confirm this opinion, I propose to call it 
Archaeocyathellus. Until, however, more can be said 
about it, T prefer to class it as above” (by “as above.” 
apparently “as Archaeocyathus” is meant). Ford’s 
specimen had slender dissepiments; it was fluted 
externally like A floreus. The name Archaeocyathellus 
does not appear to have been definitely adopted even by 
