. Ordovician fossils of north China. Paleontology; Paleontology. Vol I. Grabau—Ordovician Fossils from North China (I) 79 The inner tul)e of the siphuncle (endosiphuncle of authors) varies in diameter with the progress of siphuncular filling. In a specimen (Plate IX, fig. 4) in which the siphuncle has a width of 15 mm., it is only 1 mm. wide. In another (Plate VII, fig. 3), where the diameter of the siphuncle is about 11 mm., the open central tube has a diameter of about 5 mm. In the latter specimen, broad open diverticula diverge laterally, terminating in the centers of the nummuli, apparentl
. Ordovician fossils of north China. Paleontology; Paleontology. Vol I. Grabau—Ordovician Fossils from North China (I) 79 The inner tul)e of the siphuncle (endosiphuncle of authors) varies in diameter with the progress of siphuncular filling. In a specimen (Plate IX, fig. 4) in which the siphuncle has a width of 15 mm., it is only 1 mm. wide. In another (Plate VII, fig. 3), where the diameter of the siphuncle is about 11 mm., the open central tube has a diameter of about 5 mm. In the latter specimen, broad open diverticula diverge laterally, terminating in the centers of the nummuli, apparently in fine tubuli. In the former example, where the central tube has been narrowed to a diameter of 1 mm., the diverticula are reduced to tubes which curve obliquely downwards and outwards. Thus the tube which terminates in a pore in the center of a nummulus, reaches the endo- siphuncle at a point almost in the median horizontal plane of the nummulus next forward. This peculiar structure is seen in a weathered section from Lincheng, province of Shantung, and appears also, but in a less marked degree, in the type specimen from Manchuria figured by Freeh. It indicates that the deposition of materi- al, was most pronounced on, and finally practically confined to, the anterior part of the floor of each num- mulus as illustrated in text fig. 19. The deposits on the bottom of a single nummulus may be likened to a series of closely approximated superposed septa, the first slightly but normally concave, with a well-mar- ked siphonal funnel, and thickened at the funnel- edge ; each succeeding septum becoming more thickened at the funnel-edge, and having its funnel end invaginated into that of the preceding one. In consequence of the thickening of the septum at the funnel-edge, the central portion would rise more and more, the septum curving upwards from the rim to Fig. 19. Diagrammatic section of the part . i- ,i , ,-n of a shell of AHhv>rn;,>! rirhiiin/nii represented the funucl
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectpaleont, bookyear1922
