two Specimens of Rhynchopora Geinitziana. 127 



unwilling, however, to admit that the test is here in its original 

 condition, because the surface-layer on the left side of the valve, 

 passing on to its margin, displays a few faint black dots*; while 

 the markings are distinctly visible on the third rib, where a 

 small film-like portion of the original surface has been removed. 

 Figure 5 is a representation of what has just been described, — 

 a being the original surface, with a few Yig. 6. 



faintly-marked black dots ; and b, the /^^n^ 



abraded part, with others distinctly vi- ^^^^^*^^s^ 



sible. This absence of what may now P^£^\. 



be termed tube-apertures on the um- j^ j ^^^ y%; \ 



bone is paralleled in many specimens (r^'^''*%?>t \v 



I have examined of Terehratulidce be- ^^F^^\v\ 



longing to the Carboniferous and Per- ^^^^^\\ W 



mian systems. I have also observed it in 



Jurassic specimens. In all these cases, mineralization was pro- 

 bably the obliterating agent. Furthermore the test at the 

 umbonal portion of the small valve of the first-described speci- 

 men does not exhibit the black dots so well as the anterior 

 region : their paucity on an old part of the shell is possibly due 

 to senility. 



On the whole, I cannot but regard these two specimens as 

 completely confirming the view I took of the histology of the 

 German fossils noticed under the head of Rhynchonella Gei- 

 nitziana, in my paper already alluded to. The German speci- 

 mens, however, exhibit the tubular perforations more decidedly 

 than those from Russia, which is in favour of the latter having 

 undergone a greater amount of metamorphism. I have nothing 

 more to add to my description of the German examples : their 

 perforated structure, which is correctly represented in the plate 

 appended to my paper, is identical with that of a species of 

 Silurian Retzia, specimens of which are now before me. In the 

 latter the perforations are indicated by black dots, similar to 

 those in the German specimens. 



I therefore repeat, in conclusion, that the species under con- 

 specimen of the species, belonging to my friend M. de Verneuil, who 

 kindly lent it me for examination, shows no black dots, nor any appearance 

 of perforations; but its test has undoubtedly undergone a remarkable 

 change, which has developed a concentric structure like that of Beekite, and 

 which, in my opinion, has obliterated all indications of perforations. Another 

 specimen, collected at Ropsen, near Gera, which I procured from Mr. Damon 

 of Weymouth, diiFers remarkably, in the apjmrent absence of perforations, 

 from some, procured at the same place, which I had noticed in the " Notes " 

 already cited as published in the 'Annals.' 



* I exclude some accidental superficial black specks, which might be 

 confounded with the " black dots ;" but the latter rather appear to be in 

 the outer layer of tissue than on it. 



