104 FAMILY MILIOLIDA. 



151. JJfbnlic-^. — It will be obvious from what has preceded, that notwithstanding the 

 apparently wide interval which separates the typical Alveolina from its congeners, it has a 

 strong analogy both to Orhiculina and to Fabularia in its general plan of structure. Its 

 closest affinity, however, is evidently to the regularly spiral type of Orbiculina, since we find 

 in it no trace of that Milioline plan of growth which so remarkably characterises Fabularia. 

 It has been already pointed out that Orbiculina essentially differs from OrbitoUtes in the 

 investment of the first-formed convolutions by the latter, so that its umbilical region becomes 

 prominent instead of being depressed, and its spire coils round an axis instead of round a 

 point ; and, by tlie gradation which has been just shown to have an actual existence, the 

 progressive elongation of the axis round which the spire revolves converts the flattened 

 lenticular spiral of the J. rofella into the almost cylindrical volution of A. elonyata. The 

 difference in shape, in fact, is not nearly so great between Orbiculina adunca and A. roiella 

 as it is between A. rotella and A. ehnyata ; but it requires an examination which I have not 

 yet had the opportunity of making into the internal structure of A. rotella, to enable me to 

 affirm with certainty that the transition which it so obviously presents to the Orbicuhne 

 type in its external form extends also to its plan of growth. 



152. Geographical Bidribufion. — The recent examples of this type are limited, so far as 

 we at present know, to the seas of tropical or southern temperate regions ; the larger 

 fusiform and cylindrical forms having been chiefly brought from the shores of New Holland 

 and of the Philippine Islands in the eastern hemisphere, and from those of Cuba and the 

 Antilles in the western ; whilst a small spheroidal variety, which appears to belong to the 

 simple type, is figured by Ehrenberg (xlii, pi. xxxvii, 10, fig. 1, a—f) from the Adriatic. 



153. Geological Distribution. — The extinct forms of Alveolina belong for the most part 

 to the formations coeval with the Nummulitic Limestone ; and they present themselves in 

 various proportions, sometimes so abundantly as almost of themselves to make up the 

 substance of the deposit, in the early Tertiaries of Paris, Bordeaux, the Pyrenees, and 

 Austria, as also in those of Persia and Northern India (xix, xxi). One species is stated by 

 D'Orbigny (lxxiii, p. 145) to present itself in tlie Turonian or Lower Chalk formation at 

 the mouth of the Gironde, although none has been hitherto met with in any part of the 

 Senonian or Upper Chalk.* 



" canaliferous system " in Alveolina ; and that the appearances which have been interpreted by 

 Mr. Carter (xxi) as indicative of its presence in the fossil Alveolina of Scinde are quite comforma'ble 

 with the account of its structure which I liave given on the basis of a very careful examination of that 

 of its recent analogue. 



* I cannot agree with ray friends, Messrs. Parker and Kupert Jones (lxxx a), in referring tlie 

 Palffiozoic Fusulina to this type ; for although the metamorphic condition of the shell, in all the 

 specimens 1 have examined, forbids my speaking with full assurance, yet the appearance presented by 

 thin sections is such as to leave scarcely any doubt in my mind that its structure was tubular, and 

 that it consequently holds somewhat the same place in the hyaline series that Alveolina does ip the 

 porcellanotis . 



