Hayasaka — Richthofenia in Japan. 467 



the body chamber (cavita ventrale of Di-Stefano) 6 of 

 a conically elongated ventral valve. The dark substance 

 occupying the median elliptical area is the matrix filling 

 the chamber. The wall directly surrounding it is the 

 innermost layer of the shell, and is composed of a fine 

 lamellar tissue with silky lustre. This inner shell layer 

 is remarkably well represented in the illustrations of 

 AVaagen 7 and Di-Stefano. The median shell layer is 

 composed of small vesicular dissepiments arranged 

 vertically. Waagen calls this layer "the median cystose 

 shell layer/' while Di-Stefano names it "struttra cellu- 

 losa clello strato media." B6se s describes it as follows: 

 "It is formed by a network of cells which are constituted 

 in the lower part of the apex region by nearly hemispheri- 

 cal cysts, while on the side of the animal chamber 

 these -cells are more irregular, their bottoms being 

 directed obliquely towards above and towards the out- 

 side." In the present specimen, this median layer is 

 only partly exhibited. The outermost shell layer is 

 almost entirely broken away, although there remains a 

 very small fragment, showing its former existence. 



The shell is penetrated by numerous canals which are 

 said to pass into hollow spines projecting upon the exte- 

 rior surface of the shell. Inside the visceral chamber 

 these canals open into circular pits, each of which is lying 

 on a wart. Such warts give rise to longitudinal ridges 

 that gradually become indistinct, or fade away down- 

 wards. Such a feature is very well shown by Waagen in 

 one of his plates (fig. 7, pi. 83), while it is indicated in the 

 present thin section by the cut edges of warts and ridges. 



Just below the lower portion of the cut edge of the 

 body chamber, something like an axial region of a tetra- 

 coral is exhibited. It is a section of a part of the so- 

 called "cavita miofora" of Di-Stefano, but is not, as it 

 first appears to be, that of the lower, tabulated portion 

 of the visceral cavity, since further below the median 

 cystose layer is once more shown, this time in a nearly 

 transverse section. Vertical septa are also very indis- 

 tinctly seen. 



6 Di-Stefano : Le Rielitlwfenia dei Calcari, etc. Palaeontogr. Italia, vol. 

 20, 1914. 



7 Waagen: Product ^.s-limestone Fossils, Braehiopoda. 1885. 



8 Bose: Contributions to the Knowledge of Eichtlwfenia, etc. Bull. Univ. 

 Texas, Xo. 55, 1916. 



