Although this morphotype is small it is easy to recognise optically at magnifications between X 100 and X 150 diameters because of its most peculiar apertural system which the writer has not observed for any other taxon of the Globorotaliidae. In many ways however, the extension of the aperture into the terminal face of the last chamber might be compared to the apertural system of specimens included in the genus Clavigerinella or even hantkenine forms. However, as far as trochospirally coiled forms are concerned, it would seem no other basically turborotaliid taxon possesses an aperture which extends from the umbilicus, first as an interiomarginal slit-like opening and then, secondly, continuously into the area of the anterior terminal face of the last formed chamber usually becoming a little more widely open distally as compared to its proximal, more umbilical, part (cf. paratype of pl. 63, figs. 4 and 5). Thus, although the aperture is interiomarginal proximally, at and near the umbilical depression, the aperture is not interiomarginal distally within the area of the terminal face. This is, of course, not characteristic of the Globorotaliidae at all and on the face of it a new genus and family of the Globigerinacea ought to be erected from a strict application of morphological principles. However, it would seem from the close general similarity of the overall test morphology of longi apertura to that of specimens included in the taxon Globorotalia (Turborotalia) archeocompressa Blow, 1979, that such a strict application of morphological principles to erect a new generic (and even familial) taxonomic category would be a nega tion of the true systematisation involved in palaeontological work. Whilst the writer believes that both morphological and phylogenetic principles must always be logically invoked for the taxonomic systematisation of fossil forms, there is a need for moderation especially where a single morphotypic taxon is involved which is closely genetically linked to more morphologically usual forms. Accordingly, the writer has no hesitation in ascribing the taxon longiapertura to the subgenus Globorotalia (Turborotalia) Cushman and Bermudez, 1949, emended Blow, 1979, and disregarding the speciality of the apertural system for the supraspecific placement of the taxon. Nevertheless, the apertural system of longiapertura is a peculiar and constant feature to all the specimens of the taxon and must have taxonomic priority in the recognition of the morphotypic expression of the taxon itself.

The illustrations given on pl. 63 are mainly devoted to an analysis of the peculiarities of the apertural system. In the paratype figured on pl. 63, fig. 1, the proximal part of the aperture is obscured by a film of mounting glue which results from an original use in an assemblage slide and not in the mounting of the specimen for S.E.M. work. In this specimen, the aperture extends obliquely from the umbilicus on the left of the specimen illustration to within the area of the terminal face; in this paratype the aperture is somewhat unusually less open distally. The paratypic specimen illustrated on pl. 63, figs. 4 and 5, has lost its final (or last few?) chambers so that the opening is strictly a septal aperture. However, this septal aperture still has the form of a true final aperture and, from fig. 5, it can be seen that this form is also present for a previous septal aperture within the confines of the apertural system of the last preserved chamber. Thus, the peculiar nature of the apertural system appears to be constant for the later stages of ontogeny, at least, of forms referable to the taxon longiapertura.

"The paratypes illustrated on pl. 63, figs. 2, 3 and 6, show the constancy of the final aperture shape in other specimens where only 5 chambers are present in the final convolution. The paratype illustrated in dorsal view shows a form with 6 complete chambers present in the last whorl. Whilst the normal complement of chambers appears to be 5 1/2 in the last whorl, the range of variation encompasses forms with about 4 1/2 chambers to 6 1/2 chambers visible in the final convolution of the test; however, the extremes of variation are only rarely occurring. The specmens referable to the taxon are, however, not uncommon and despite its small size it is an easily recognised morphotype even optically at magnifications of about X ca. 100 diameters. For this reason it has been chosen as the nominate taxon for Zone P. but it must be emphasized that the morphotype ranges with reduced frequency into Zone P.1 (Subzone P. la only).

Of the other paratypes illustrated on pls. 56, 58, 68 and 72, the specimens on p1. 56, figs. 3 and 4 and pl. 72, fig. 1, are worthy of further comment. Thus, the specimen on pl. 72, fig. 1, shows 6 1/2 chambers present in the final convolution of the test whilst the specimen figured on pl. 56, figs. 3 and 4, is a little more tightly coiled than usually seen for other specimens.
""The structure and texture of the wall in specimens referred to G. (T) longiapertura Blow, 1979, is absolutely similar to that seen in specimens referred to G. (T) archeocompressa Blow, 1979 which possesses a more completely normal turborotaliid apertural-system. As far as is known from the writer's present observations, the wall structure is microgranular but with a preferred orientation of the `C-optical axes of the microgranules normal to the test wall so that there is no difference in wall struc ture in specimens referable to longiapertura Blow, 1979 as compared to that seen in specimens referable to archeocompressa Blow, 1979, and indeed to that seen in specimens referable to the whole of the G. (T) compressa (sensu law) lineage (Blow, 1979, op. cit., pp. 1061-1069). The sparse distribution of very fine mural-pores in specimens referable to longiapertura is also virtually identical to that seen for specimens referable to archeocompressa and other representatives of the compressa (sensu law) lineage. From this, the writer concludes that longiapertura, notwithstanding its peculiar apertural-system, is really a primitive member of the compressa (sensu lato) evolutionary gens and is, thereby, correctly considered as being a taxon to be included in the subgenus Globorotalia (Turborotalia).
The specimen figured on pl. 68, figs. 1 and 2 (Blow, 1979, op. cit.), and referred to as cf. longiapertura? does not show the distal extension of the apertural system but does show an apertural system fundamentally similar to that seen for typical longiapertura. However, the form called cf. longiapertura? does provide a link with the forms called Globorotalia (T.) cf. tetragona (Morozova) figured on pl. 64, fig. 7 and pl. 67, fig. 5 (Blow, 1979, op. cit.), which have a much tighter coiling-mode than seen in longiapertura. Thus, it may be that the derivation of longiapertura is from the morphotypes called G. (T) cf. tetragona via the forms of longiapertura which are a little more tightly coiled than usual, such as that paratype figured on pl. 56, fig. 3, to, eventually, the typical longiapertura which has quite an open and reasonably lax coiling-mode.

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