upper Palaeozoic and Mesozoic Fossils. 329 



P. cinctus is recognized by the nearly circular outline, with 

 fairly small, sub-equal auricles. The sui'face of the valves is 

 broken up by thin, concentric laminae, more or less erect, and 

 the shell is ornamented with fine, closely-set, radial striae. 

 Auricles strongly marked with closely-set ridges, slightly 

 flexuose. Right valve a little more convex than the left. 



The outer layer of the shell has in some cases been almost 

 entirely removed, and the intermediate layej* shows weathered 

 out on its surface a plexus of ramifying tunnels, now infilled with 

 matrix ; they are most probably the work of a parasitic boring 

 organism (? fungus), but coarser than either Duncan's Palaeachlya 

 or Bornet and Flahault's Ostracoblabe. The average diameter 

 of these tubes is about 0.4 mm. Besides this, there also occurs 

 in one of the shells a much coarser kind of perforation, which 

 does not confine itself to one layer of the shell but passes through 

 at all angles, and its character makes it presumably referable to 

 a l)oring sponge of the family Clionidae. Neither of these 

 borings yield any residual structure which would assist in their 

 identification. 



Locality and Horizon. — Greenough River District, Western 

 Australia. Jurassic. [2062]. 



Ctenostreon, Eichwald. 



Ctenostreon pectinifopmis, Schlotheim, sp. 



(PI. XXX., Fig 1). 



Ostracites pectiniformis, Schlotheim, 1820. Petrefactenkunde, 

 i., p. 231. 



Lima proboscidea, Sow., 1821. Min. Conch. Gt. Brit., vol. iii., 

 p. 115, pi. cclxiv. 



Moore, 1870. Quart. Journ. Geol. Soc, vol. xxvi., pp. 231, 

 232. 



Ctenostreon pectiniformis (Schloth.), Etheridge, Jun., 1901. 

 Records Austr. Mus., vol. iv., No. 1, p. 14. 



There is a left valve representing the above species in the 

 Daiutree and Gregory collection, which at first sight seemed to 

 present almost specific differences from the specimens already 

 figured by the above-named authors, and others mentioned in 



