| OCR Text |
Show 1895.] FORAMINIFERA FROM THE ARABIAN SEA. 47 transverse sections of the tests (see fig. 12). In all cases those observed consisted of two chambers, and they are exactly comparable in shape with the early chambers of the adult specimens, which, by the way, belong to the megalospheric type of growth. In a paper on " If Amphistegina del calcare lenticolare di Par-lascio" 2, Dr. G. A. de Amicis described a form of Amphistegina formerly named Nummulites targionii by Professor Meneghini, but which is shown by Dr. de Amicis to be a true Amphistegina. It appears to approach very closely in its general characters to A. radiata, which it especially resembles in the subdivision of the peripheral margins of the successive layers seen in transverse section2. The specimens of A. radiata found in the Arabian Sea average § of an inch in diameter, and are thus somewhat larger than the specimens originally described by Fichtel and Moll. The usual number of principal septa appearing on the surface of full-grown individuals is from eighteen to twenty, and these septa often show a tendency to bifurcate towards the periphery. The surface of the test is tolerably smooth, and the septal lines are marked out in clear transparent shell-matter, while the rest of the test is of a creamy-white colour. Incidentally I may mention that although the form which has been referred to as Nummulina cumingii by Drs. Carpenter and Brady has not occurred in these deposits, I have no doubt that, as Professor Rupert Jones has already suggested to me, that species is more properly referable to the " Nautilus venosus" of Fichtel and Moll, and should perhaps stand as Nummulina venosa (F. & M.). It is open to some question, however, whether it is a truly Nummuline form, since some published drawings of the species show a decidedly inequilateral growth, and in point of fact a series of specimens may show all gradations into Operculina. Amphistegina radiata was found only in Sample No. 2, in which it was common. OPERCULINA, d'Orbigny. 274. OPERCULINA COMPLANATA (Defrance). Lenticulites complanata, Defrance, 1822, Diet. Sci. Nat. vol. xxv. p. 453. Operculina arabica, Carter, 1853, Journ. Roy. Asiatic Soc, Bombay Branch, vol. iv. p. 437, pi. xviii. Operculina complanata, Brady, 1884, Chall. Rep. vol. ix. p. 743, pi. cxii. figs. 3-5, 8. The above species was described under the name of 0. arabica by H . J. Carter, who obtained his specimens off the south-east coast of Arabia. Found in Sample No. 1, frequent. 1 1885. Processi verbali della Societa Toscana di Scienze Naturali. 2 See also D e Amicis, 1886, " II Calcare ad Amphistegina nella Provincia di Pisa," Atti Soc. Toscana Sci. Wat., Memorie, vol. vii. pi. xi. figs. 1, 3, 6, 7. |
