Vol I. 



Grabau Ordovician Fossils from North China 



(0 79 



The inner tube 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), 

 whore 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, whore 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 



of a shell of .!'(/..,> ,,,/,//,,,/ represented the funnel-edge, until the center of the septum, still 



on plate IX, lijr. 4. drawn to scale. The 



iphniicle is here shown in the process of filling pierced by the funnel-holes, is higher than the rim. 



by Bterooplasm. In the upper part it is shown 



empty, smvrssive layer* of stereopiasm are This would mean a progressive collapse of the 



lidded, in such a way that the diverticula from 



8i P honal expansions, until they represented only a 

 thin double membrane. Some slight additions of 

 lime have meanwhile been made to the inside of the 

 upper (forward) surface of the inside of the nummu- 

 lus, by the upper surface of the siphonal expansion. Thus, what appears as a lateral tube 

 in section, may in reality be the section of the space occupied by this collapsed siphonal 



tural si/e. (<, camera' ; ih; diverticula of endo- 

 .-iplmtuKc: en, endosiphotube; x, septa; *h, 

 shrill </, stcreuplasinic filling of nummuli). 



