576 
DE. CAEPEXTEE’S EESEAECHES OX THE F0EA3IIXIFEEA. 
Hence the analogy of Operciilina atfords good ground to surmise that many of the 
reputed species in the nearly-allied genus ISummulites have no real title to that rank ; 
the differences among many of them being not nearly so great as those we have met 
mth among the varieties of Operculina ; whilst those presented by many others do not 
exceed what might be reasonably expected to occur under a greater variety of modifying 
agencies. But I have shown 162) that it may be fairly questioned whether there 
is adequate ground for upholding the generic distinctness of Operculina and Xummulifes ; 
the characteristic by which the latter has been asserted to be specially distinguished 
being not unfrequently observable as a varietal difference in the former. The form 
which I have described under the designation of Amphistegina Cumingii* bears a 
striking resemblance to the ordinary Nummuline type in the early part of its growth, 
and to the ordinary Operculine in the later ; and may be regarded as in many respects 
a connecting link between the two. 
247. There appears, then, strong reason for considering Cydoclypeus, Heterosfegina, 
Opei'culina, Xummulites, and Ampliistegina as related to each other in the same manner 
and degree as the leading forms already enumerated under the Orbiculine group. And 
it is very curious to observe the perfect analogy which prevails in regard to the forms 
under which these two great types of structure — essentially different as they are — tend 
to develope themselves. As I have just pointed out, the relation of Cydoclypeus to 
Heterostegina is exactly that of Orhitolites to OrhiciiJina. So if the transverse or secondary 
septa of Heterostegina were undeveloped, we should have an Operculina, Xum?nulina, or 
Ampliistegina (these three types being in my "view essentially one and the same), just as 
the like deficiency actually occurring in Orhiculina gives to it all the essential characters 
of Peneroplis. And the parallelism seems to be completed by the existence in Fusulina\ 
of the same elongated condition of this type, that AlveoJina is of the Orbiculine. 
248. The mutual accordance of all these in the highly elaborated texture of the shell, 
in the relation which this bears to the segments of the sarcode-body, and in the presence 
of an intermediate skeleton with its canal-system, is extremely close. The substance of 
the shell is very dense, and of almost vitreous transparence where it is not perforated by 
the minute closely-set tubuli which usually pass direct from the ulterior of the chambers 
towards the external surface. Each segment of the body has its own proper envelope, 
so that the septa between the chambers are composed of two distinct lamimr, which 
diverge from each other where they give passage to the canal-system, and which are 
often further separated by the intervention of a portion of the “ intermediate skeleton.” 
The passages of communication between the chambers are so narrow, that the segments 
* It is questioned by Messrs. Paeker and Eupert Joxes wbetlier this is a true Ampldstegina, chiefly on 
account of its bilateral symmetry (Ann. of Nat. Hist. Feb. 1860, p. 111). But I have met Avith perfect 
bilateral symmetry in specimens warranted as Ampldstegince by those excellent judges of that type. 
t I have not yet been able to satisfy myself as to the precise affinities of FusuJina, the mctamorphic con- 
dition of its shell interfering witli the minute study of its structure ; but my view of its nature essentially 
corresponds with that of Messrs. Parker and Eupert Jokes. (Sec Quart. Journ. of Geol. Soc., Nov. 1860, 
p. 458.) 
