3 
Blake cites ZitteFs figure as a synonym of his Macrocephalites typicus 
(p. 42). The large example of this species (PI. Ill, fig. 1) which, though 
Blake does not say so, is presumably the type, is distinctly flexiradiate — 
it differs from ZitteFs figure by the greater coarseness of ribbing; but if 
ZitteFs figure is a much reduced one this difference would vanish. 1 Blake’s 
PI. Ill, f. 1, will now be taken as the lectotype of Macrocephalites typicus , 
for the young specimens which he figures (PI. Ill, f. 2; PI. IV, f. 5) are 
different by being decidedly recticostate. It might be argued that recti- 
costation is a true feature of young forms, being changed later to flexi- 
costation. This is possible, but Blake gives no evidence: a specimen or 
specimens showing such a change would have been the necessary proof. 
On the contrary he figures by the same name of M. typicus (PL III, fig. 3) 
another example of about the size required — this shows flexicostation chang- 
ing to recticostation. Further, there is no evidence of suture-line to prove 
that all these forms belong to one species. Nor is suture-line given by 
Blake for his large shell, so that, however like this specimen may be ZitteFs 
figure, there is, taking account of homceomorphy, no certain proof of iden- 
tity. Blake, on the other hand, mentions (II, p. 42) a specimen from 
“Peterborough (No. 27)” which “shows the last suture followed by a 
complete whorl.” This specimen is in the collection of the Geological 
Survey of England (No. 8651) and on it is a label relating to the suture-line 
saying “Diagram 4.” In Fig. 4, Blake (p, 46), is a reproduction of the 
suture-line of this specimen; but Blake has omitted to say anything about 
it: the title of Fig. 4 “Adult suture-line of Macrocephalites compressus ” 
can only refer to the large suture-line. This large one is very different 
from the small one — the former could be called “deeply divided”; the 
latter could not — it is particularly simple. Such a suture-line cannot allow 
the specimen to agree with ZitteFs description. This specimen is the 
one that I have referred to above as so like ZitteFs figure, but differing 
from his description in its simple suture-line. 
The exact identification of the genotype of Macrocephalites is a neces- 
sary prelude to any determination as to which family the genus should 
belong and, also, as to whether species of Macrocephalitoid aspect can be 
grouped in the same family. How easily homceomorphy may mislead in 
this respect can be judged from the forms which Zittel cited as examples 
of his genus. He says (p. 470) that about 40 species belong to it, among 
them A. morrisi Oppel which is now placed in the family Tulitidae S. 
Buckman (3, p. 43), A. keppleri Opp. which Neumayr and TJhlig separated 
as Kepplerites (p. 53) recognizing its affinity to Cosmoceras (Kosmoeera- 
tidae, Hyatt, S. Buckman, 3, p. 53). The Macrocephalitoid aspect of 
certain adult Kosmoceratids is an interesting phenomenon; these Kosmo- 
ceratids and the Macrocephali occur at about the same date, which may be 
a ‘cause of trouble. 
From the above remarks it is obvious that the palaeontological part 
of this investigation is by no means simple. The same may be said of the 
investigation in its chronological aspect. In a general way the Macro- 
cephali of Europe are known to be about of the date of the upper Corn- 
brash-lower Kellaways of England or B athonian-C alio vian border-line of 
continental geologists. But when more exact information is required, as 
1 See, however, page 8. 
